<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2023 Workiva-->
<!--r:48861f38-a660-4561-953e-2e5bf0546dfb,g:a5a227f7-ebd2-4535-a93f-1bd838fd738d-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://synchronoss.com/role/Cover" xlink:type="simple" xlink:href="sncr-20230930.xsd#Cover"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_69335191-78f2-4456-866c-37ac1e332181" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_DocumentType_69335191-78f2-4456-866c-37ac1e332181" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_b95ae6be-2d9d-47fe-b15f-dddae2e5e257" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_DocumentQuarterlyReport_b95ae6be-2d9d-47fe-b15f-dddae2e5e257" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_552f6bdd-5738-4b37-bafa-97f3f08cd489" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_DocumentPeriodEndDate_552f6bdd-5738-4b37-bafa-97f3f08cd489" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_78361a15-cbf4-4bac-a188-799ae1f2de60" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_DocumentTransitionReport_78361a15-cbf4-4bac-a188-799ae1f2de60" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_fe28fafb-4d41-41fc-ab6d-662d3e891b42" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_EntityFileNumber_fe28fafb-4d41-41fc-ab6d-662d3e891b42" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_57b33b60-48dc-4cca-a517-6e0323e93dbe" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_EntityRegistrantName_57b33b60-48dc-4cca-a517-6e0323e93dbe" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_8c3a1650-1921-43f1-b1cd-019241912186" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_EntityIncorporationStateCountryCode_8c3a1650-1921-43f1-b1cd-019241912186" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_d4232c11-667c-4944-a585-2245612965da" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_EntityTaxIdentificationNumber_d4232c11-667c-4944-a585-2245612965da" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_3d0b6bc1-8bea-4ef6-bc9d-499908ea8f2d" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_EntityAddressAddressLine1_3d0b6bc1-8bea-4ef6-bc9d-499908ea8f2d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_7dbdd4db-3788-42e5-976a-e738b254cbf7" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_EntityAddressAddressLine2_7dbdd4db-3788-42e5-976a-e738b254cbf7" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_e3c050c6-0975-4ac5-9721-050614a7bf79" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_EntityAddressCityOrTown_e3c050c6-0975-4ac5-9721-050614a7bf79" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_d644e792-35dd-41e4-8d22-2619ff9408eb" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_EntityAddressStateOrProvince_d644e792-35dd-41e4-8d22-2619ff9408eb" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_667c55f4-24e6-404d-a8bd-9dedcd6844b2" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_EntityAddressPostalZipCode_667c55f4-24e6-404d-a8bd-9dedcd6844b2" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_8486e8d7-f732-4085-b235-bb86cf22d301" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_CityAreaCode_8486e8d7-f732-4085-b235-bb86cf22d301" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_212d98b4-ebb9-495b-976a-209feb12f251" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_LocalPhoneNumber_212d98b4-ebb9-495b-976a-209feb12f251" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_4afc61e6-be62-401f-9e78-30eca1a72377" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_EntityCurrentReportingStatus_4afc61e6-be62-401f-9e78-30eca1a72377" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_4533ebb4-9f0d-4468-904e-e90cfa40e830" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_EntityInteractiveDataCurrent_4533ebb4-9f0d-4468-904e-e90cfa40e830" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_970d71c1-f46d-41ac-9ac7-4122e5065bf4" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_EntityFilerCategory_970d71c1-f46d-41ac-9ac7-4122e5065bf4" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_ea9178d0-159d-41ea-84fc-875e45bbe0ed" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_EntitySmallBusiness_ea9178d0-159d-41ea-84fc-875e45bbe0ed" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_3d008271-62f2-4665-9390-3e1d9ff23bd3" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_EntityEmergingGrowthCompany_3d008271-62f2-4665-9390-3e1d9ff23bd3" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_12702543-c881-4d98-b472-d0a8ca2c1295" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_EntityShellCompany_12702543-c881-4d98-b472-d0a8ca2c1295" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_27e92755-55e5-4b43-a06f-1e40db7caf3c" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_Security12bTitle_27e92755-55e5-4b43-a06f-1e40db7caf3c" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_6faf6632-0589-4ade-a776-825fb9a1cfa8" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_TradingSymbol_6faf6632-0589-4ade-a776-825fb9a1cfa8" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_fff2a414-c719-4cba-ab26-2e66c1abc334" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_SecurityExchangeName_fff2a414-c719-4cba-ab26-2e66c1abc334" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_a42d062a-eb1d-46d8-90a3-0f5db33b53ba" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_a42d062a-eb1d-46d8-90a3-0f5db33b53ba" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_73afddcb-dc63-4779-9d28-ce3a00de7d52" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_EntityCentralIndexKey_73afddcb-dc63-4779-9d28-ce3a00de7d52" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_1d624852-02f6-4404-90f7-22d96c82339b" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_AmendmentFlag_1d624852-02f6-4404-90f7-22d96c82339b" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_b018e9bb-9529-4568-af06-c303823361f8" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_CurrentFiscalYearEndDate_b018e9bb-9529-4568-af06-c303823361f8" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_a7d9c0d2-7bea-4281-b4b3-8c2a481a1a14" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_DocumentFiscalYearFocus_a7d9c0d2-7bea-4281-b4b3-8c2a481a1a14" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_d6b1c7ef-2239-4a29-ac0e-9aece8d8872b" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_DocumentFiscalPeriodFocus_d6b1c7ef-2239-4a29-ac0e-9aece8d8872b" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_d50bd1d8-6974-4c16-8065-7ffbe14a439c" xlink:href="https://xbrl.sec.gov/dei/2023/dei-2023.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_a16e9fde-e6c2-47d1-8b79-740d23db5a09" xlink:to="loc_dei_DocumentInformationTable_d50bd1d8-6974-4c16-8065-7ffbe14a439c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_f83696ad-9d81-491d-b182-1c0d3c4cbf3c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_d50bd1d8-6974-4c16-8065-7ffbe14a439c" xlink:to="loc_us-gaap_StatementClassOfStockAxis_f83696ad-9d81-491d-b182-1c0d3c4cbf3c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_f83696ad-9d81-491d-b182-1c0d3c4cbf3c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_f83696ad-9d81-491d-b182-1c0d3c4cbf3c" xlink:to="loc_us-gaap_ClassOfStockDomain_f83696ad-9d81-491d-b182-1c0d3c4cbf3c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_3a518d41-eeb9-492c-a38c-41dc987e6cf4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_f83696ad-9d81-491d-b182-1c0d3c4cbf3c" xlink:to="loc_us-gaap_ClassOfStockDomain_3a518d41-eeb9-492c-a38c-41dc987e6cf4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_36e97a9b-75d0-4335-b14d-b7fc30269877" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_3a518d41-eeb9-492c-a38c-41dc987e6cf4" xlink:to="loc_us-gaap_CommonStockMember_36e97a9b-75d0-4335-b14d-b7fc30269877" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_EightPointThreeSevenFivePercent2500ParValueSeniorNotesDue2026Member_487bcbab-5913-4ad3-a681-e6b8c4625c55" xlink:href="sncr-20230930.xsd#sncr_EightPointThreeSevenFivePercent2500ParValueSeniorNotesDue2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_3a518d41-eeb9-492c-a38c-41dc987e6cf4" xlink:to="loc_sncr_EightPointThreeSevenFivePercent2500ParValueSeniorNotesDue2026Member_487bcbab-5913-4ad3-a681-e6b8c4625c55" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSUnaudited" xlink:type="simple" xlink:href="sncr-20230930.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETSUnaudited"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_fd0ed8ef-c038-4b3f-82ab-5259ff36a45e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_cffeebfa-d91d-40c2-af81-fa7514c2fb7b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fd0ed8ef-c038-4b3f-82ab-5259ff36a45e" xlink:to="loc_us-gaap_AssetsAbstract_cffeebfa-d91d-40c2-af81-fa7514c2fb7b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_f4923a35-805b-4dfe-a7b9-99c071d63de8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_cffeebfa-d91d-40c2-af81-fa7514c2fb7b" xlink:to="loc_us-gaap_AssetsCurrentAbstract_f4923a35-805b-4dfe-a7b9-99c071d63de8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_d188fb35-8847-4512-a58a-9460885b420e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_f4923a35-805b-4dfe-a7b9-99c071d63de8" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_d188fb35-8847-4512-a58a-9460885b420e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_98e17107-d55d-43fa-a71e-ad8d7774937c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_f4923a35-805b-4dfe-a7b9-99c071d63de8" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_98e17107-d55d-43fa-a71e-ad8d7774937c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_4b3a4540-a72e-4dc6-8c2c-c9848fb2e4bf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_f4923a35-805b-4dfe-a7b9-99c071d63de8" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_4b3a4540-a72e-4dc6-8c2c-c9848fb2e4bf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_65ab1416-22e8-4569-ac34-8d690a694e69" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_f4923a35-805b-4dfe-a7b9-99c071d63de8" xlink:to="loc_us-gaap_AssetsCurrent_65ab1416-22e8-4569-ac34-8d690a694e69" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNoncurrentAbstract_3135cecd-a92f-46af-8da0-551cee09a1c4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_cffeebfa-d91d-40c2-af81-fa7514c2fb7b" xlink:to="loc_us-gaap_AssetsNoncurrentAbstract_3135cecd-a92f-46af-8da0-551cee09a1c4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_3eceb34c-a88b-4287-a410-c647a321be84" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_3135cecd-a92f-46af-8da0-551cee09a1c4" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_3eceb34c-a88b-4287-a410-c647a321be84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_d5a5abbb-5bf2-4318-8864-ee1a398cc694" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_3135cecd-a92f-46af-8da0-551cee09a1c4" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_d5a5abbb-5bf2-4318-8864-ee1a398cc694" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_a32e23c7-0d03-42e3-ab86-ebf5fd49fef4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_3135cecd-a92f-46af-8da0-551cee09a1c4" xlink:to="loc_us-gaap_Goodwill_a32e23c7-0d03-42e3-ab86-ebf5fd49fef4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_b58b0d04-7c47-4942-aaa8-871b8c3688ae" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_3135cecd-a92f-46af-8da0-551cee09a1c4" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_b58b0d04-7c47-4942-aaa8-871b8c3688ae" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesAndLoansReceivableNetNoncurrent_87cd6f6c-23bd-425d-8558-d8af609019dc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NotesAndLoansReceivableNetNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_3135cecd-a92f-46af-8da0-551cee09a1c4" xlink:to="loc_us-gaap_NotesAndLoansReceivableNetNoncurrent_87cd6f6c-23bd-425d-8558-d8af609019dc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_2337051c-52b3-4d3d-86dc-593a2e55d3e3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_3135cecd-a92f-46af-8da0-551cee09a1c4" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_2337051c-52b3-4d3d-86dc-593a2e55d3e3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNoncurrent_30f435ea-c0ac-4787-9aa1-fa5e67f5ac50" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_3135cecd-a92f-46af-8da0-551cee09a1c4" xlink:to="loc_us-gaap_AssetsNoncurrent_30f435ea-c0ac-4787-9aa1-fa5e67f5ac50" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_6f649996-1813-40d6-82d0-a2110994a155" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_cffeebfa-d91d-40c2-af81-fa7514c2fb7b" xlink:to="loc_us-gaap_Assets_6f649996-1813-40d6-82d0-a2110994a155" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_8af037f2-d4b7-4bba-99bd-1bfdfbe6248e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fd0ed8ef-c038-4b3f-82ab-5259ff36a45e" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_8af037f2-d4b7-4bba-99bd-1bfdfbe6248e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_6e633d25-c88e-4b87-a367-50b5bd8b17ce" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_8af037f2-d4b7-4bba-99bd-1bfdfbe6248e" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_6e633d25-c88e-4b87-a367-50b5bd8b17ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_90d1dcaa-7a4c-4f89-88ae-cdf1bfd2a103" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_6e633d25-c88e-4b87-a367-50b5bd8b17ce" xlink:to="loc_us-gaap_AccountsPayableCurrent_90d1dcaa-7a4c-4f89-88ae-cdf1bfd2a103" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_82d42a8a-d247-4c0f-9555-eb41cee69bb1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_6e633d25-c88e-4b87-a367-50b5bd8b17ce" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_82d42a8a-d247-4c0f-9555-eb41cee69bb1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_1a38c066-02ba-4764-89f7-87d089e17b3e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_6e633d25-c88e-4b87-a367-50b5bd8b17ce" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_1a38c066-02ba-4764-89f7-87d089e17b3e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_589eba3e-b287-407c-a5dd-4fde9d39154d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_6e633d25-c88e-4b87-a367-50b5bd8b17ce" xlink:to="loc_us-gaap_LiabilitiesCurrent_589eba3e-b287-407c-a5dd-4fde9d39154d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_bb00ce80-12d4-4b8a-8da2-c81f1149dcba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_8af037f2-d4b7-4bba-99bd-1bfdfbe6248e" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_bb00ce80-12d4-4b8a-8da2-c81f1149dcba" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_03fe75a7-4b05-43f4-9942-3000ede6fc05" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_8af037f2-d4b7-4bba-99bd-1bfdfbe6248e" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_03fe75a7-4b05-43f4-9942-3000ede6fc05" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_784dccf2-1748-47ec-be07-d6d89e7ad082" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ContractWithCustomerLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_8af037f2-d4b7-4bba-99bd-1bfdfbe6248e" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_784dccf2-1748-47ec-be07-d6d89e7ad082" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_LeaseLiabilityNoncurrent_02f1dbc8-592d-4902-9cdb-5a95dfd1d8e3" xlink:href="sncr-20230930.xsd#sncr_LeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_8af037f2-d4b7-4bba-99bd-1bfdfbe6248e" xlink:to="loc_sncr_LeaseLiabilityNoncurrent_02f1dbc8-592d-4902-9cdb-5a95dfd1d8e3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_43d8636d-b600-4b25-8391-cd7f8cb7996c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_8af037f2-d4b7-4bba-99bd-1bfdfbe6248e" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_43d8636d-b600-4b25-8391-cd7f8cb7996c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_986c8fa9-742a-4098-bd25-0ae3454cfbfa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_8af037f2-d4b7-4bba-99bd-1bfdfbe6248e" xlink:to="loc_us-gaap_Liabilities_986c8fa9-742a-4098-bd25-0ae3454cfbfa" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_353895b1-8653-4cfe-8142-9cedcbb0430c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_8af037f2-d4b7-4bba-99bd-1bfdfbe6248e" xlink:to="loc_us-gaap_CommitmentsAndContingencies_353895b1-8653-4cfe-8142-9cedcbb0430c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_8fef322c-f579-41f8-b76b-0581eab0ea82" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_8af037f2-d4b7-4bba-99bd-1bfdfbe6248e" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_8fef322c-f579-41f8-b76b-0581eab0ea82" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_102523ab-abc7-4056-8233-90a0107a1960" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_8af037f2-d4b7-4bba-99bd-1bfdfbe6248e" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityCarryingAmount_102523ab-abc7-4056-8233-90a0107a1960" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_c8c9c7c2-da20-4aac-a6d9-1b209fb280a5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_8af037f2-d4b7-4bba-99bd-1bfdfbe6248e" xlink:to="loc_us-gaap_StockholdersEquityAbstract_c8c9c7c2-da20-4aac-a6d9-1b209fb280a5" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_818a8ec7-30fe-4ef7-b2cc-45bede41ad7c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_c8c9c7c2-da20-4aac-a6d9-1b209fb280a5" xlink:to="loc_us-gaap_CommonStockValue_818a8ec7-30fe-4ef7-b2cc-45bede41ad7c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_32ee8fa9-41fb-420a-8335-1c3e68fd952e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_c8c9c7c2-da20-4aac-a6d9-1b209fb280a5" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_32ee8fa9-41fb-420a-8335-1c3e68fd952e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_e0945e5d-9367-4c14-9923-a755d72220d2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_c8c9c7c2-da20-4aac-a6d9-1b209fb280a5" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_e0945e5d-9367-4c14-9923-a755d72220d2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_480c0000-f593-485f-b745-7ee080ef54ea" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_c8c9c7c2-da20-4aac-a6d9-1b209fb280a5" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_480c0000-f593-485f-b745-7ee080ef54ea" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_860c7de3-63e3-4c5c-b42b-7ea51aaa9575" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_c8c9c7c2-da20-4aac-a6d9-1b209fb280a5" xlink:to="loc_us-gaap_StockholdersEquity_860c7de3-63e3-4c5c-b42b-7ea51aaa9575" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_31af97f2-1214-4807-89e0-fed660b62f25" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_8af037f2-d4b7-4bba-99bd-1bfdfbe6248e" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_31af97f2-1214-4807-89e0-fed660b62f25" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_0fc73425-5e31-4672-9d3f-5dd34473e2dc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_fd0ed8ef-c038-4b3f-82ab-5259ff36a45e" xlink:to="loc_us-gaap_StatementTable_0fc73425-5e31-4672-9d3f-5dd34473e2dc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_fe2a5c48-1935-4466-adfc-9b55ed25e80a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_0fc73425-5e31-4672-9d3f-5dd34473e2dc" xlink:to="loc_us-gaap_StatementClassOfStockAxis_fe2a5c48-1935-4466-adfc-9b55ed25e80a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_fe2a5c48-1935-4466-adfc-9b55ed25e80a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_fe2a5c48-1935-4466-adfc-9b55ed25e80a" xlink:to="loc_us-gaap_ClassOfStockDomain_fe2a5c48-1935-4466-adfc-9b55ed25e80a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_16a28350-1613-4960-b69d-2bbb666555a3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_fe2a5c48-1935-4466-adfc-9b55ed25e80a" xlink:to="loc_us-gaap_ClassOfStockDomain_16a28350-1613-4960-b69d-2bbb666555a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesBPreferredStockMember_b632a233-9899-45a6-b8fb-d874827cd15e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeriesBPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_16a28350-1613-4960-b69d-2bbb666555a3" xlink:to="loc_us-gaap_SeriesBPreferredStockMember_b632a233-9899-45a6-b8fb-d874827cd15e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSUnauditedParenthetical" xlink:type="simple" xlink:href="sncr-20230930.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETSUnauditedParenthetical"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSUnauditedParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_3fe41f36-d577-4ce3-a11e-78403f4e9fa4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityParOrStatedValuePerShare_fceaf485-8f1c-4d68-9ca4-eee5080d0f7e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3fe41f36-d577-4ce3-a11e-78403f4e9fa4" xlink:to="loc_us-gaap_TemporaryEquityParOrStatedValuePerShare_fceaf485-8f1c-4d68-9ca4-eee5080d0f7e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesAuthorized_1e1224e0-3705-4399-947b-c39ea41d2b95" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquitySharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3fe41f36-d577-4ce3-a11e-78403f4e9fa4" xlink:to="loc_us-gaap_TemporaryEquitySharesAuthorized_1e1224e0-3705-4399-947b-c39ea41d2b95" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesIssued_e2de6db3-a8b7-41da-accc-094c215de0b1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquitySharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3fe41f36-d577-4ce3-a11e-78403f4e9fa4" xlink:to="loc_us-gaap_TemporaryEquitySharesIssued_e2de6db3-a8b7-41da-accc-094c215de0b1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_6e6d6be8-b551-4dfc-95bc-85f4b1ec4e7f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3fe41f36-d577-4ce3-a11e-78403f4e9fa4" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_6e6d6be8-b551-4dfc-95bc-85f4b1ec4e7f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_e9774883-fb82-4d3d-ad9b-ee2579b7e134" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3fe41f36-d577-4ce3-a11e-78403f4e9fa4" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_e9774883-fb82-4d3d-ad9b-ee2579b7e134" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_8392dcf1-8c01-46c1-84e5-52db6caff762" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3fe41f36-d577-4ce3-a11e-78403f4e9fa4" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_8392dcf1-8c01-46c1-84e5-52db6caff762" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_7714522d-c04e-432b-9298-8836602728df" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3fe41f36-d577-4ce3-a11e-78403f4e9fa4" xlink:to="loc_us-gaap_CommonStockSharesIssued_7714522d-c04e-432b-9298-8836602728df" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_f956a6f2-a052-4baf-ac0f-0e3137d4e01a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3fe41f36-d577-4ce3-a11e-78403f4e9fa4" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_f956a6f2-a052-4baf-ac0f-0e3137d4e01a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_6641d077-654e-45f7-8b9a-7f800f937175" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_3fe41f36-d577-4ce3-a11e-78403f4e9fa4" xlink:to="loc_us-gaap_StatementTable_6641d077-654e-45f7-8b9a-7f800f937175" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_a214503c-b97f-48ea-8296-152df55f0742" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_6641d077-654e-45f7-8b9a-7f800f937175" xlink:to="loc_us-gaap_StatementClassOfStockAxis_a214503c-b97f-48ea-8296-152df55f0742" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_a214503c-b97f-48ea-8296-152df55f0742_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_a214503c-b97f-48ea-8296-152df55f0742" xlink:to="loc_us-gaap_ClassOfStockDomain_a214503c-b97f-48ea-8296-152df55f0742_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_5e731ac9-6831-4ac3-967b-914fe7e2b73f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_a214503c-b97f-48ea-8296-152df55f0742" xlink:to="loc_us-gaap_ClassOfStockDomain_5e731ac9-6831-4ac3-967b-914fe7e2b73f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesBPreferredStockMember_d9ece34a-efc2-4c04-9eb8-073486fe443c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeriesBPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_5e731ac9-6831-4ac3-967b-914fe7e2b73f" xlink:to="loc_us-gaap_SeriesBPreferredStockMember_d9ece34a-efc2-4c04-9eb8-073486fe443c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITYUnaudited" xlink:type="simple" xlink:href="sncr-20230930.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITYUnaudited"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITYUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_edc5a0f8-2d2f-4a45-a484-9a7a650dbf1d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4c5c508a-a37f-4e96-a9fe-762e823ffd72" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_edc5a0f8-2d2f-4a45-a484-9a7a650dbf1d" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4c5c508a-a37f-4e96-a9fe-762e823ffd72" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_cdcefaf0-73ef-420e-ba79-5beac8ca79c2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4c5c508a-a37f-4e96-a9fe-762e823ffd72" xlink:to="loc_us-gaap_CommonStockSharesIssued_cdcefaf0-73ef-420e-ba79-5beac8ca79c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_c4b34240-ea49-4d52-9d0d-349d6850446f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4c5c508a-a37f-4e96-a9fe-762e823ffd72" xlink:to="loc_us-gaap_StockholdersEquity_c4b34240-ea49-4d52-9d0d-349d6850446f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_31a89cdc-b7e9-4dee-95bb-ee8937317cbf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4c5c508a-a37f-4e96-a9fe-762e823ffd72" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_31a89cdc-b7e9-4dee-95bb-ee8937317cbf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_cfb39c16-4888-45db-acad-5d652ce13a7b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4c5c508a-a37f-4e96-a9fe-762e823ffd72" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_cfb39c16-4888-45db-acad-5d652ce13a7b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPreferredStock_90bd8a48-8b9a-49ff-8f9d-20ed7d78f1ee" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DividendsPreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4c5c508a-a37f-4e96-a9fe-762e823ffd72" xlink:to="loc_us-gaap_DividendsPreferredStock_90bd8a48-8b9a-49ff-8f9d-20ed7d78f1ee" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts_a4126d0e-302f-40cc-8fb9-3eb461c93d98" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4c5c508a-a37f-4e96-a9fe-762e823ffd72" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts_a4126d0e-302f-40cc-8fb9-3eb461c93d98" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_475869a4-ffc9-46d7-923e-e61d3e312a3a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4c5c508a-a37f-4e96-a9fe-762e823ffd72" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_475869a4-ffc9-46d7-923e-e61d3e312a3a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_dc3579fb-b86e-4c67-83b9-99644d3f2106" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4c5c508a-a37f-4e96-a9fe-762e823ffd72" xlink:to="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_dc3579fb-b86e-4c67-83b9-99644d3f2106" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_19a66fd1-ba8e-450a-bbbb-f69f4c664c06" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4c5c508a-a37f-4e96-a9fe-762e823ffd72" xlink:to="loc_us-gaap_ProfitLoss_19a66fd1-ba8e-450a-bbbb-f69f4c664c06" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestChangeInRedemptionValue_6829f660-7606-44ae-88de-34dda26ad5d7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_MinorityInterestChangeInRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4c5c508a-a37f-4e96-a9fe-762e823ffd72" xlink:to="loc_us-gaap_MinorityInterestChangeInRedemptionValue_6829f660-7606-44ae-88de-34dda26ad5d7" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_34266ccd-4b22-437c-8db8-269ddf707db4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_4c5c508a-a37f-4e96-a9fe-762e823ffd72" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_34266ccd-4b22-437c-8db8-269ddf707db4" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_a78943c7-30ec-4395-8f52-53106977c792" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_684ac90a-e9ee-414d-92f8-d54519189ca4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_eb1632e7-f180-4576-b22d-8b75ff1a30b8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_edc5a0f8-2d2f-4a45-a484-9a7a650dbf1d" xlink:to="loc_us-gaap_StatementTable_eb1632e7-f180-4576-b22d-8b75ff1a30b8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_08e44182-3666-4921-823e-941013c94c7e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_eb1632e7-f180-4576-b22d-8b75ff1a30b8" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_08e44182-3666-4921-823e-941013c94c7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_08e44182-3666-4921-823e-941013c94c7e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_08e44182-3666-4921-823e-941013c94c7e" xlink:to="loc_us-gaap_EquityComponentDomain_08e44182-3666-4921-823e-941013c94c7e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_2cba035a-7ad5-43a6-96bf-670331c6eb7d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_08e44182-3666-4921-823e-941013c94c7e" xlink:to="loc_us-gaap_EquityComponentDomain_2cba035a-7ad5-43a6-96bf-670331c6eb7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_cab2d109-8e75-4698-9d57-4f8459b0f84b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_2cba035a-7ad5-43a6-96bf-670331c6eb7d" xlink:to="loc_us-gaap_CommonStockMember_cab2d109-8e75-4698-9d57-4f8459b0f84b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_d308c2e1-44a9-4522-bb60-d13fd25d2216" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_2cba035a-7ad5-43a6-96bf-670331c6eb7d" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_d308c2e1-44a9-4522-bb60-d13fd25d2216" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_7504ae9a-05cc-40e4-b37e-f1a9cc55ca96" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_2cba035a-7ad5-43a6-96bf-670331c6eb7d" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_7504ae9a-05cc-40e4-b37e-f1a9cc55ca96" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_2acc06f8-8d20-4155-84f0-660bf32b1fb4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_2cba035a-7ad5-43a6-96bf-670331c6eb7d" xlink:to="loc_us-gaap_RetainedEarningsMember_2acc06f8-8d20-4155-84f0-660bf32b1fb4" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUnaudited" xlink:type="simple" xlink:href="sncr-20230930.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUnaudited"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUnaudited" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_3b3839ec-eada-4afb-9f0e-1f5a4e1a3aeb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_acad1481-701b-4f5a-9f6c-5ac82803c4bc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3839ec-eada-4afb-9f0e-1f5a4e1a3aeb" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_acad1481-701b-4f5a-9f6c-5ac82803c4bc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_b5938386-9994-4944-a6c9-34db08b482d8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_acad1481-701b-4f5a-9f6c-5ac82803c4bc" xlink:to="loc_us-gaap_ProfitLoss_b5938386-9994-4944-a6c9-34db08b482d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c9fbde67-b4b2-4824-ab91-ac930d1af9c8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_acad1481-701b-4f5a-9f6c-5ac82803c4bc" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c9fbde67-b4b2-4824-ab91-ac930d1af9c8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DepreciationDepletionAndAmortizationNetOfImpairment_2cd22919-59ff-4e86-a360-a9a14e2fbf2f" xlink:href="sncr-20230930.xsd#sncr_DepreciationDepletionAndAmortizationNetOfImpairment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c9fbde67-b4b2-4824-ab91-ac930d1af9c8" xlink:to="loc_sncr_DepreciationDepletionAndAmortizationNetOfImpairment_2cd22919-59ff-4e86-a360-a9a14e2fbf2f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_64a8846c-ac95-4c2a-9e45-5b9df931f12f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c9fbde67-b4b2-4824-ab91-ac930d1af9c8" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_64a8846c-ac95-4c2a-9e45-5b9df931f12f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnDispositionOfAssets_b99329f4-0d77-4412-bab8-1bb0ebc684e4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GainLossOnDispositionOfAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c9fbde67-b4b2-4824-ab91-ac930d1af9c8" xlink:to="loc_us-gaap_GainLossOnDispositionOfAssets_b99329f4-0d77-4412-bab8-1bb0ebc684e4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfBusiness_8313d093-7089-4f17-ad36-1fc80092e09c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GainLossOnSaleOfBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c9fbde67-b4b2-4824-ab91-ac930d1af9c8" xlink:to="loc_us-gaap_GainLossOnSaleOfBusiness_8313d093-7089-4f17-ad36-1fc80092e09c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfDebtDiscountPremium_b2c30b97-77e7-46f8-8a50-a21970d6ae54" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AmortizationOfDebtDiscountPremium"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c9fbde67-b4b2-4824-ab91-ac930d1af9c8" xlink:to="loc_us-gaap_AmortizationOfDebtDiscountPremium_b2c30b97-77e7-46f8-8a50-a21970d6ae54" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_b6895776-37f2-490c-825f-2d4a8bcb1669" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c9fbde67-b4b2-4824-ab91-ac930d1af9c8" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_b6895776-37f2-490c-825f-2d4a8bcb1669" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_e71aeaa2-d8ad-46fe-863d-a1143b21b003" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c9fbde67-b4b2-4824-ab91-ac930d1af9c8" xlink:to="loc_us-gaap_ShareBasedCompensation_e71aeaa2-d8ad-46fe-863d-a1143b21b003" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ImpairmentOfLoanAndSTIReceivable_a298506c-106c-4213-a2e3-26c4e243a03d" xlink:href="sncr-20230930.xsd#sncr_ImpairmentOfLoanAndSTIReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c9fbde67-b4b2-4824-ab91-ac930d1af9c8" xlink:to="loc_sncr_ImpairmentOfLoanAndSTIReceivable_a298506c-106c-4213-a2e3-26c4e243a03d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseImpairmentLoss_e9e181b0-f79f-4405-920e-603a111509fc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OperatingLeaseImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c9fbde67-b4b2-4824-ab91-ac930d1af9c8" xlink:to="loc_us-gaap_OperatingLeaseImpairmentLoss_e9e181b0-f79f-4405-920e-603a111509fc" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_f8bedb00-2bab-47df-a856-cc9f2ef16879" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_c9fbde67-b4b2-4824-ab91-ac930d1af9c8" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_f8bedb00-2bab-47df-a856-cc9f2ef16879" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_0b007565-02b5-46ad-94dc-ffb9d79877a4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_f8bedb00-2bab-47df-a856-cc9f2ef16879" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_0b007565-02b5-46ad-94dc-ffb9d79877a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_2d7a83cf-fc08-4f3a-8e95-0986aaf45d9a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_f8bedb00-2bab-47df-a856-cc9f2ef16879" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_2d7a83cf-fc08-4f3a-8e95-0986aaf45d9a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_de799c73-ee9c-4221-b108-54a87e018e0e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_f8bedb00-2bab-47df-a856-cc9f2ef16879" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_de799c73-ee9c-4221-b108-54a87e018e0e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_632c7bde-fd54-4840-91af-52f7e246b7e6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_f8bedb00-2bab-47df-a856-cc9f2ef16879" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_632c7bde-fd54-4840-91af-52f7e246b7e6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_db546289-a73e-4724-9494-99d6cd24f0c4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_f8bedb00-2bab-47df-a856-cc9f2ef16879" xlink:to="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_db546289-a73e-4724-9494-99d6cd24f0c4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_3193f598-5dcf-4676-a678-5073af5e00c3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInOtherOperatingLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_f8bedb00-2bab-47df-a856-cc9f2ef16879" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_3193f598-5dcf-4676-a678-5073af5e00c3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_706d0ff6-982c-4dda-9382-69aaec348f96" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_acad1481-701b-4f5a-9f6c-5ac82803c4bc" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_706d0ff6-982c-4dda-9382-69aaec348f96" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_bd0b7887-af09-40f3-bf6f-0b99c2b4080c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3839ec-eada-4afb-9f0e-1f5a4e1a3aeb" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_bd0b7887-af09-40f3-bf6f-0b99c2b4080c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_e3964581-6194-41e0-82f0-ceb45c3fb471" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_bd0b7887-af09-40f3-bf6f-0b99c2b4080c" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_e3964581-6194-41e0-82f0-ceb45c3fb471" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForSoftware_45c350a5-d44f-49f7-b867-7092750f6c0e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsForSoftware"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_bd0b7887-af09-40f3-bf6f-0b99c2b4080c" xlink:to="loc_us-gaap_PaymentsForSoftware_45c350a5-d44f-49f7-b867-7092750f6c0e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_9954a392-7569-4d8e-9bf0-573368875b0d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromDivestitureOfBusinesses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_bd0b7887-af09-40f3-bf6f-0b99c2b4080c" xlink:to="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_9954a392-7569-4d8e-9bf0-573368875b0d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_2f43d95f-9327-4945-a0b7-ed7dd461a014" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_bd0b7887-af09-40f3-bf6f-0b99c2b4080c" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_2f43d95f-9327-4945-a0b7-ed7dd461a014" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_0dd29b1a-0f1f-4c5e-a87c-35f269c046ae" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3839ec-eada-4afb-9f0e-1f5a4e1a3aeb" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_0dd29b1a-0f1f-4c5e-a87c-35f269c046ae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_6a2ad822-54a4-4bf7-a255-8b9084543763" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_0dd29b1a-0f1f-4c5e-a87c-35f269c046ae" xlink:to="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_6a2ad822-54a4-4bf7-a255-8b9084543763" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ProceedsFromAccountsReceivableFacility_2675f3ad-b436-408d-ad01-123a1a577f63" xlink:href="sncr-20230930.xsd#sncr_ProceedsFromAccountsReceivableFacility"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_0dd29b1a-0f1f-4c5e-a87c-35f269c046ae" xlink:to="loc_sncr_ProceedsFromAccountsReceivableFacility_2675f3ad-b436-408d-ad01-123a1a577f63" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_RepaymentsOfAccountsReceivableFacility_4fca7d9a-621a-4952-8bcf-622d7e9f4ffa" xlink:href="sncr-20230930.xsd#sncr_RepaymentsOfAccountsReceivableFacility"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_0dd29b1a-0f1f-4c5e-a87c-35f269c046ae" xlink:to="loc_sncr_RepaymentsOfAccountsReceivableFacility_4fca7d9a-621a-4952-8bcf-622d7e9f4ffa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock_df0d41b5-a67e-4f17-8fa6-9c709761e8d1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_0dd29b1a-0f1f-4c5e-a87c-35f269c046ae" xlink:to="loc_us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock_df0d41b5-a67e-4f17-8fa6-9c709761e8d1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRepurchaseOfRedeemableConvertiblePreferredStock_efca5249-6266-4b7e-987a-b7267dff6fe7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsForRepurchaseOfRedeemableConvertiblePreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_0dd29b1a-0f1f-4c5e-a87c-35f269c046ae" xlink:to="loc_us-gaap_PaymentsForRepurchaseOfRedeemableConvertiblePreferredStock_efca5249-6266-4b7e-987a-b7267dff6fe7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_8340dc46-d5aa-4cb2-8f56-26091272bb76" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_0dd29b1a-0f1f-4c5e-a87c-35f269c046ae" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_8340dc46-d5aa-4cb2-8f56-26091272bb76" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_4fe51dbf-92f7-48ad-a525-0b4814a1e4cf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3839ec-eada-4afb-9f0e-1f5a4e1a3aeb" xlink:to="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_4fe51dbf-92f7-48ad-a525-0b4814a1e4cf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_dd3d6346-b24a-47ef-a64e-46941101eb43" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3839ec-eada-4afb-9f0e-1f5a4e1a3aeb" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_dd3d6346-b24a-47ef-a64e-46941101eb43" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_6535aff7-56b8-4118-8bb2-4a3a674e12c3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3839ec-eada-4afb-9f0e-1f5a4e1a3aeb" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_6535aff7-56b8-4118-8bb2-4a3a674e12c3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_96399dea-90a1-4b02-8d4f-ec9ba04ca63f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_a76a9043-500f-4007-befe-e4071a0d202f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NoncashInvestingAndFinancingItemsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3b3839ec-eada-4afb-9f0e-1f5a4e1a3aeb" xlink:to="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_a76a9043-500f-4007-befe-e4071a0d202f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPreferredStockPaidinkind_6cdf6fe4-a70e-4208-b0e9-bd1b10c5e8c1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DividendsPreferredStockPaidinkind"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_a76a9043-500f-4007-befe-e4071a0d202f" xlink:to="loc_us-gaap_DividendsPreferredStockPaidinkind_6cdf6fe4-a70e-4208-b0e9-bd1b10c5e8c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_43957c51-0969-49a4-9f9e-4cb0fc886132" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_3b3839ec-eada-4afb-9f0e-1f5a4e1a3aeb" xlink:to="loc_us-gaap_StatementTable_43957c51-0969-49a4-9f9e-4cb0fc886132" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_d57c41a7-3c92-44dd-85ae-a46bbe36b559" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_43957c51-0969-49a4-9f9e-4cb0fc886132" xlink:to="loc_us-gaap_StatementClassOfStockAxis_d57c41a7-3c92-44dd-85ae-a46bbe36b559" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_d57c41a7-3c92-44dd-85ae-a46bbe36b559_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_d57c41a7-3c92-44dd-85ae-a46bbe36b559" xlink:to="loc_us-gaap_ClassOfStockDomain_d57c41a7-3c92-44dd-85ae-a46bbe36b559_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_cbbef37a-10dc-450a-9912-12e437f0514f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_d57c41a7-3c92-44dd-85ae-a46bbe36b559" xlink:to="loc_us-gaap_ClassOfStockDomain_cbbef37a-10dc-450a-9912-12e437f0514f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesBPreferredStockMember_251e5e05-78ea-47c9-98e5-72a3207a406f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeriesBPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_cbbef37a-10dc-450a-9912-12e437f0514f" xlink:to="loc_us-gaap_SeriesBPreferredStockMember_251e5e05-78ea-47c9-98e5-72a3207a406f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/CapitalStructureTables" xlink:type="simple" xlink:href="sncr-20230930.xsd#CapitalStructureTables"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CapitalStructureTables" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4d42c9ea-fe92-4738-897f-45986a8962c1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityTableTextBlock_b889623d-7c97-4eda-8ea7-acd1065ca344" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4d42c9ea-fe92-4738-897f-45986a8962c1" xlink:to="loc_us-gaap_TemporaryEquityTableTextBlock_b889623d-7c97-4eda-8ea7-acd1065ca344" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCompensationCostForShareBasedPaymentArrangementsAllocationOfShareBasedCompensationCostsByPlanTableTextBlock_6345e38e-5dd9-4a1e-9a74-0fecece89e6d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfCompensationCostForShareBasedPaymentArrangementsAllocationOfShareBasedCompensationCostsByPlanTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4d42c9ea-fe92-4738-897f-45986a8962c1" xlink:to="loc_us-gaap_ScheduleOfCompensationCostForShareBasedPaymentArrangementsAllocationOfShareBasedCompensationCostsByPlanTableTextBlock_6345e38e-5dd9-4a1e-9a74-0fecece89e6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock_17aaff0a-35f0-4850-8483-7a702ef6b4aa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4d42c9ea-fe92-4738-897f-45986a8962c1" xlink:to="loc_us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock_17aaff0a-35f0-4850-8483-7a702ef6b4aa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock_67f2b188-35e6-43de-b5ca-bfab26a0d837" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4d42c9ea-fe92-4738-897f-45986a8962c1" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock_67f2b188-35e6-43de-b5ca-bfab26a0d837" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonvestedRestrictedStockSharesActivityTableTextBlock_5544f2a8-7073-4f49-a455-5199a85fb3ba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NonvestedRestrictedStockSharesActivityTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4d42c9ea-fe92-4738-897f-45986a8962c1" xlink:to="loc_us-gaap_NonvestedRestrictedStockSharesActivityTableTextBlock_5544f2a8-7073-4f49-a455-5199a85fb3ba" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_22d484ec-ef7d-441e-9b66-d4e717e92afa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4d42c9ea-fe92-4738-897f-45986a8962c1" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_22d484ec-ef7d-441e-9b66-d4e717e92afa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_f2a9bb8d-6028-4fcf-b461-68049626492a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_22d484ec-ef7d-441e-9b66-d4e717e92afa" xlink:to="loc_us-gaap_AwardTypeAxis_f2a9bb8d-6028-4fcf-b461-68049626492a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f2a9bb8d-6028-4fcf-b461-68049626492a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_f2a9bb8d-6028-4fcf-b461-68049626492a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f2a9bb8d-6028-4fcf-b461-68049626492a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_16994a71-4ed5-4fe7-a531-181b2dd7b907" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_f2a9bb8d-6028-4fcf-b461-68049626492a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_16994a71-4ed5-4fe7-a531-181b2dd7b907" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_a2231cd9-8f5a-407b-b053-45d6441ff2fe" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_16994a71-4ed5-4fe7-a531-181b2dd7b907" xlink:to="loc_us-gaap_RestrictedStockMember_a2231cd9-8f5a-407b-b053-45d6441ff2fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_bd83ec92-ee4d-4a79-a6f9-0f1c23256cff" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_16994a71-4ed5-4fe7-a531-181b2dd7b907" xlink:to="loc_us-gaap_PerformanceSharesMember_bd83ec92-ee4d-4a79-a6f9-0f1c23256cff" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/DescriptionofBusinessDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#DescriptionofBusinessDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/DescriptionofBusinessDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionLineItems_4efce827-6464-4650-9b5a-9f3a445ece40" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionConsiderationTransferred_a55e2793-03b4-4c94-b9a1-d7936ab481e1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetAcquisitionConsiderationTransferred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionLineItems_4efce827-6464-4650-9b5a-9f3a445ece40" xlink:to="loc_us-gaap_AssetAcquisitionConsiderationTransferred_a55e2793-03b4-4c94-b9a1-d7936ab481e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionTable_e0113256-c5e2-4a91-bb86-5aed6b3540c0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AssetAcquisitionLineItems_4efce827-6464-4650-9b5a-9f3a445ece40" xlink:to="loc_us-gaap_AssetAcquisitionTable_e0113256-c5e2-4a91-bb86-5aed6b3540c0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionAxis_46aa6131-750d-443a-8fae-865346c8a0cd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AssetAcquisitionTable_e0113256-c5e2-4a91-bb86-5aed6b3540c0" xlink:to="loc_us-gaap_AssetAcquisitionAxis_46aa6131-750d-443a-8fae-865346c8a0cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_46aa6131-750d-443a-8fae-865346c8a0cd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AssetAcquisitionAxis_46aa6131-750d-443a-8fae-865346c8a0cd" xlink:to="loc_us-gaap_AssetAcquisitionDomain_46aa6131-750d-443a-8fae-865346c8a0cd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_7a20d2bb-c18b-4b46-8ba0-e717b89904dd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AssetAcquisitionAxis_46aa6131-750d-443a-8fae-865346c8a0cd" xlink:to="loc_us-gaap_AssetAcquisitionDomain_7a20d2bb-c18b-4b46-8ba0-e717b89904dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_MessagingAndDigitalBusinessesMember_5d2377a7-6305-4350-82a2-a6fdef92ecf4" xlink:href="sncr-20230930.xsd#sncr_MessagingAndDigitalBusinessesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionDomain_7a20d2bb-c18b-4b46-8ba0-e717b89904dd" xlink:to="loc_sncr_MessagingAndDigitalBusinessesMember_5d2377a7-6305-4350-82a2-a6fdef92ecf4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_99ce8e2b-5424-4bdc-96e3-ee4fa6ef3140" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AssetAcquisitionTable_e0113256-c5e2-4a91-bb86-5aed6b3540c0" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_99ce8e2b-5424-4bdc-96e3-ee4fa6ef3140" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_99ce8e2b-5424-4bdc-96e3-ee4fa6ef3140_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_99ce8e2b-5424-4bdc-96e3-ee4fa6ef3140" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_99ce8e2b-5424-4bdc-96e3-ee4fa6ef3140_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_b27ec8d8-386c-4dbd-89e8-314a7d83ed82" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_99ce8e2b-5424-4bdc-96e3-ee4fa6ef3140" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_b27ec8d8-386c-4dbd-89e8-314a7d83ed82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_b7b54abb-9a80-4788-9699-5eb784f1c351" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_b27ec8d8-386c-4dbd-89e8-314a7d83ed82" xlink:to="loc_us-gaap_SubsequentEventMember_b7b54abb-9a80-4788-9699-5eb784f1c351" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/BasisofPresentationandConsolidationDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#BasisofPresentationandConsolidationDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/BasisofPresentationandConsolidationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_adc055e5-965f-4dde-8fe6-b9706e4e3d7c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_adc055e5-965f-4dde-8fe6-b9706e4e3d7c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DisposalGroupIncludingDiscontinuedOperationReceivable_3c5431af-fc1d-4af4-b89b-070e3de79a0b" xlink:href="sncr-20230930.xsd#sncr_DisposalGroupIncludingDiscontinuedOperationReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_sncr_DisposalGroupIncludingDiscontinuedOperationReceivable_3c5431af-fc1d-4af4-b89b-070e3de79a0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DisposalGroupIncludingDiscontinuedOperationEscrowDeposit_612e9044-0377-45c7-93fb-edb66309a56e" xlink:href="sncr-20230930.xsd#sncr_DisposalGroupIncludingDiscontinuedOperationEscrowDeposit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_sncr_DisposalGroupIncludingDiscontinuedOperationEscrowDeposit_612e9044-0377-45c7-93fb-edb66309a56e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DisposalGroupIncludingDiscontinuedOperationDisbursementToBeReceived12MonthsFromClosingDate_a5b9f0a1-9479-4700-9efc-6c19b3b4b1e7" xlink:href="sncr-20230930.xsd#sncr_DisposalGroupIncludingDiscontinuedOperationDisbursementToBeReceived12MonthsFromClosingDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_sncr_DisposalGroupIncludingDiscontinuedOperationDisbursementToBeReceived12MonthsFromClosingDate_a5b9f0a1-9479-4700-9efc-6c19b3b4b1e7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DisposalGroupIncludingDiscontinuedOperationContingentConsideration_e3c8972e-4ef6-4292-a2af-bc17a9418718" xlink:href="sncr-20230930.xsd#sncr_DisposalGroupIncludingDiscontinuedOperationContingentConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_sncr_DisposalGroupIncludingDiscontinuedOperationContingentConsideration_e3c8972e-4ef6-4292-a2af-bc17a9418718" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_c0318194-b01a-4123-adaf-a128e60f9c8b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ProceedsFromDivestitureOfBusinesses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_us-gaap_ProceedsFromDivestitureOfBusinesses_c0318194-b01a-4123-adaf-a128e60f9c8b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DisposalGroupIncludingDiscontinuedOperationAdditionalEscrowDeposit_1169310e-b9be-4010-9bbc-c3ae150d0f7d" xlink:href="sncr-20230930.xsd#sncr_DisposalGroupIncludingDiscontinuedOperationAdditionalEscrowDeposit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_sncr_DisposalGroupIncludingDiscontinuedOperationAdditionalEscrowDeposit_1169310e-b9be-4010-9bbc-c3ae150d0f7d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DisposalGroupIncludingDiscontinuedOperationFairValueOfEarnOutProvision_9148618a-2559-4811-85a0-509bf9e2b5eb" xlink:href="sncr-20230930.xsd#sncr_DisposalGroupIncludingDiscontinuedOperationFairValueOfEarnOutProvision"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_sncr_DisposalGroupIncludingDiscontinuedOperationFairValueOfEarnOutProvision_9148618a-2559-4811-85a0-509bf9e2b5eb" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationIntangibleAssets_751263a0-9c06-4b69-afcb-1936d0a644d0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationIntangibleAssets_751263a0-9c06-4b69-afcb-1936d0a644d0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGoodwill1_217fcfd6-bd66-4947-b3c3-e6d265887d16" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationGoodwill1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGoodwill1_217fcfd6-bd66-4947-b3c3-e6d265887d16" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnSaleOfBusiness_2921c9e8-c872-4e90-b2e2-d51f8fe481c8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_GainLossOnSaleOfBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_us-gaap_GainLossOnSaleOfBusiness_2921c9e8-c872-4e90-b2e2-d51f8fe481c8" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableFromSecuritization_eda7a2f6-5510-4728-8671-f92de39c9fde" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccountsReceivableFromSecuritization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_us-gaap_AccountsReceivableFromSecuritization_eda7a2f6-5510-4728-8671-f92de39c9fde" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_5cc8a939-2770-44ad-96f2-da67b1aaa43e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_5cc8a939-2770-44ad-96f2-da67b1aaa43e" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_76323ccf-f09d-445a-9d84-4e1cc0f9639e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_76323ccf-f09d-445a-9d84-4e1cc0f9639e" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_fe484f8c-759b-47ad-894a-7ff905fb9b10" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LineOfCreditFacilityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_fe484f8c-759b-47ad-894a-7ff905fb9b10" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ProceedsFromAccountsReceivableFacility_c8174053-7f8c-4b08-94c1-fa61ed5ab8a2" xlink:href="sncr-20230930.xsd#sncr_ProceedsFromAccountsReceivableFacility"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_sncr_ProceedsFromAccountsReceivableFacility_c8174053-7f8c-4b08-94c1-fa61ed5ab8a2" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeReceivablesHeldForSaleAmount_5508cef9-1191-48b0-a9d0-5f4c370069fc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TradeReceivablesHeldForSaleAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_us-gaap_TradeReceivablesHeldForSaleAmount_5508cef9-1191-48b0-a9d0-5f4c370069fc" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_c16df88c-37f5-4d6a-8bed-dd01396c8d78" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_71788aa6-a3df-43c9-a4c7-c2012293db17" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_c16df88c-37f5-4d6a-8bed-dd01396c8d78" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_889b1dde-56b9-4868-88a7-12ef0e7294aa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_c16df88c-37f5-4d6a-8bed-dd01396c8d78" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_889b1dde-56b9-4868-88a7-12ef0e7294aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_889b1dde-56b9-4868-88a7-12ef0e7294aa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_889b1dde-56b9-4868-88a7-12ef0e7294aa" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_889b1dde-56b9-4868-88a7-12ef0e7294aa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_88d5e08d-391e-461c-be75-c83b53263cc9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_889b1dde-56b9-4868-88a7-12ef0e7294aa" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_88d5e08d-391e-461c-be75-c83b53263cc9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DXPBusinessMember_3e4c5536-ab1d-493a-a136-499f86a9af46" xlink:href="sncr-20230930.xsd#sncr_DXPBusinessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_88d5e08d-391e-461c-be75-c83b53263cc9" xlink:to="loc_sncr_DXPBusinessMember_3e4c5536-ab1d-493a-a136-499f86a9af46" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_a8943fd3-4cce-4e69-ad0b-c6a9213963ee" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_c16df88c-37f5-4d6a-8bed-dd01396c8d78" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_a8943fd3-4cce-4e69-ad0b-c6a9213963ee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_a8943fd3-4cce-4e69-ad0b-c6a9213963ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_a8943fd3-4cce-4e69-ad0b-c6a9213963ee" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_a8943fd3-4cce-4e69-ad0b-c6a9213963ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_a64cc6da-824e-4fd8-a1b8-091c94ebf246" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_a8943fd3-4cce-4e69-ad0b-c6a9213963ee" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_a64cc6da-824e-4fd8-a1b8-091c94ebf246" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember_8c03bf5e-0642-4071-942c-adc719dcfb34" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_a64cc6da-824e-4fd8-a1b8-091c94ebf246" xlink:to="loc_us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember_8c03bf5e-0642-4071-942c-adc719dcfb34" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember_c09f4904-760d-4214-bb7e-ad632c65b25c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_a64cc6da-824e-4fd8-a1b8-091c94ebf246" xlink:to="loc_us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember_c09f4904-760d-4214-bb7e-ad632c65b25c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_6721e103-36e4-46bb-9ae8-26fd2aafe002" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_c16df88c-37f5-4d6a-8bed-dd01396c8d78" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_6721e103-36e4-46bb-9ae8-26fd2aafe002" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_6721e103-36e4-46bb-9ae8-26fd2aafe002_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_6721e103-36e4-46bb-9ae8-26fd2aafe002" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_6721e103-36e4-46bb-9ae8-26fd2aafe002_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_78c9a870-55e5-452d-b551-d9157c53825f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_6721e103-36e4-46bb-9ae8-26fd2aafe002" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_78c9a870-55e5-452d-b551-d9157c53825f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCurrentAssetsMember_18524ca7-04d3-4343-b36b-1f3c16d227cf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherCurrentAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_78c9a870-55e5-452d-b551-d9157c53825f" xlink:to="loc_us-gaap_OtherCurrentAssetsMember_18524ca7-04d3-4343-b36b-1f3c16d227cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_e945a1ed-4d6a-4ae1-9964-65f15e13ce97" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_c16df88c-37f5-4d6a-8bed-dd01396c8d78" xlink:to="loc_us-gaap_VariableRateAxis_e945a1ed-4d6a-4ae1-9964-65f15e13ce97" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_e945a1ed-4d6a-4ae1-9964-65f15e13ce97_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_e945a1ed-4d6a-4ae1-9964-65f15e13ce97" xlink:to="loc_us-gaap_VariableRateDomain_e945a1ed-4d6a-4ae1-9964-65f15e13ce97_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_ce23f620-eaa0-438c-aae0-de87789108a0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_e945a1ed-4d6a-4ae1-9964-65f15e13ce97" xlink:to="loc_us-gaap_VariableRateDomain_ce23f620-eaa0-438c-aae0-de87789108a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_HanoverRateMember_55f3eb7e-5614-404e-a500-a75f69582da0" xlink:href="sncr-20230930.xsd#sncr_HanoverRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_ce23f620-eaa0-438c-aae0-de87789108a0" xlink:to="loc_sncr_HanoverRateMember_55f3eb7e-5614-404e-a500-a75f69582da0" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/RevenueDisaggregationofRevenueDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#RevenueDisaggregationofRevenueDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/RevenueDisaggregationofRevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_d8e3d188-3121-4a71-8682-ba17a8b4c1ac" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_35a4101e-03da-4344-860e-6debcaa39261" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_d8e3d188-3121-4a71-8682-ba17a8b4c1ac" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_35a4101e-03da-4344-860e-6debcaa39261" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_9ea8d96c-a1b6-4e77-9f68-81bf03c7e7ac" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_d8e3d188-3121-4a71-8682-ba17a8b4c1ac" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_9ea8d96c-a1b6-4e77-9f68-81bf03c7e7ac" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_4c1adb8b-a678-4f35-b634-61f637a28040" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_9ea8d96c-a1b6-4e77-9f68-81bf03c7e7ac" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_4c1adb8b-a678-4f35-b634-61f637a28040" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_4c1adb8b-a678-4f35-b634-61f637a28040_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_4c1adb8b-a678-4f35-b634-61f637a28040" xlink:to="loc_us-gaap_SegmentDomain_4c1adb8b-a678-4f35-b634-61f637a28040_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_4edf950b-9cb3-456a-aa38-ed0e170b76ac" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_4c1adb8b-a678-4f35-b634-61f637a28040" xlink:to="loc_us-gaap_SegmentDomain_4edf950b-9cb3-456a-aa38-ed0e170b76ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_CloudMember_30e086ea-289f-469d-a098-7abe3bc20b31" xlink:href="sncr-20230930.xsd#sncr_CloudMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_4edf950b-9cb3-456a-aa38-ed0e170b76ac" xlink:to="loc_sncr_CloudMember_30e086ea-289f-469d-a098-7abe3bc20b31" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_NetworkXMember_737f8471-10cf-4f59-9782-8c9a9c83bbd8" xlink:href="sncr-20230930.xsd#sncr_NetworkXMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_4edf950b-9cb3-456a-aa38-ed0e170b76ac" xlink:to="loc_sncr_NetworkXMember_737f8471-10cf-4f59-9782-8c9a9c83bbd8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_MessagingMember_9fa15b53-9d3e-49d4-a7bc-4faf5643eafd" xlink:href="sncr-20230930.xsd#sncr_MessagingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_4edf950b-9cb3-456a-aa38-ed0e170b76ac" xlink:to="loc_sncr_MessagingMember_9fa15b53-9d3e-49d4-a7bc-4faf5643eafd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_a9f9a20d-7e77-406a-b0e3-96c9f2ed7139" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_9ea8d96c-a1b6-4e77-9f68-81bf03c7e7ac" xlink:to="loc_srt_StatementGeographicalAxis_a9f9a20d-7e77-406a-b0e3-96c9f2ed7139" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_a9f9a20d-7e77-406a-b0e3-96c9f2ed7139_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_a9f9a20d-7e77-406a-b0e3-96c9f2ed7139" xlink:to="loc_srt_SegmentGeographicalDomain_a9f9a20d-7e77-406a-b0e3-96c9f2ed7139_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_60c2d834-d685-4cea-8d2f-9d2873fe91e8" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_a9f9a20d-7e77-406a-b0e3-96c9f2ed7139" xlink:to="loc_srt_SegmentGeographicalDomain_60c2d834-d685-4cea-8d2f-9d2873fe91e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AmericasMember_062e4b4d-b5b0-4ced-ba85-aedd1cf91c0b" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_AmericasMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_60c2d834-d685-4cea-8d2f-9d2873fe91e8" xlink:to="loc_srt_AmericasMember_062e4b4d-b5b0-4ced-ba85-aedd1cf91c0b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AsiaPacificMember_af6dd385-0795-4914-b961-c16c8d8ddcd1" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_AsiaPacificMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_60c2d834-d685-4cea-8d2f-9d2873fe91e8" xlink:to="loc_srt_AsiaPacificMember_af6dd385-0795-4914-b961-c16c8d8ddcd1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EMEAMember_253754dd-44ba-406d-8dc7-f5e1f44523ff" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EMEAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_60c2d834-d685-4cea-8d2f-9d2873fe91e8" xlink:to="loc_us-gaap_EMEAMember_253754dd-44ba-406d-8dc7-f5e1f44523ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_1ca0cf0e-deee-40e6-90ce-07a976539900" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_9ea8d96c-a1b6-4e77-9f68-81bf03c7e7ac" xlink:to="loc_srt_ProductOrServiceAxis_1ca0cf0e-deee-40e6-90ce-07a976539900" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_1ca0cf0e-deee-40e6-90ce-07a976539900_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_1ca0cf0e-deee-40e6-90ce-07a976539900" xlink:to="loc_srt_ProductsAndServicesDomain_1ca0cf0e-deee-40e6-90ce-07a976539900_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_790d2172-900d-4c57-9e0b-6cb3c851c188" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_1ca0cf0e-deee-40e6-90ce-07a976539900" xlink:to="loc_srt_ProductsAndServicesDomain_790d2172-900d-4c57-9e0b-6cb3c851c188" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ProfessionalServicesMember_e9efc08e-b804-42ee-a89e-8ffb0e3ea947" xlink:href="sncr-20230930.xsd#sncr_ProfessionalServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_790d2172-900d-4c57-9e0b-6cb3c851c188" xlink:to="loc_sncr_ProfessionalServicesMember_e9efc08e-b804-42ee-a89e-8ffb0e3ea947" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TransactionServicesMember_c281fa9a-ee61-436d-8f30-c233265e5c4a" xlink:href="sncr-20230930.xsd#sncr_TransactionServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_790d2172-900d-4c57-9e0b-6cb3c851c188" xlink:to="loc_sncr_TransactionServicesMember_c281fa9a-ee61-436d-8f30-c233265e5c4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_SubscriptionServicesMember_0feffa6a-0500-4e0f-89e4-295412d7e607" xlink:href="sncr-20230930.xsd#sncr_SubscriptionServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_790d2172-900d-4c57-9e0b-6cb3c851c188" xlink:to="loc_sncr_SubscriptionServicesMember_0feffa6a-0500-4e0f-89e4-295412d7e607" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicenseMember_6189d3df-6cf0-4a76-b473-e877c853f737" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_790d2172-900d-4c57-9e0b-6cb3c851c188" xlink:to="loc_us-gaap_LicenseMember_6189d3df-6cf0-4a76-b473-e877c853f737" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/RevenueRemainingPerformanceObligationsDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#RevenueRemainingPerformanceObligationsDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/RevenueRemainingPerformanceObligationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_2c9fedc8-2b70-421e-b355-3dc222deb960" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_501b31fc-2364-4b78-901a-02f09ba31bd1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_2c9fedc8-2b70-421e-b355-3dc222deb960" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_501b31fc-2364-4b78-901a-02f09ba31bd1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_19681164-6cca-4b4b-8543-d26828123e31" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_2c9fedc8-2b70-421e-b355-3dc222deb960" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_19681164-6cca-4b4b-8543-d26828123e31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_6e42c329-7fcc-4874-87ba-01dffbbea609" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_2c9fedc8-2b70-421e-b355-3dc222deb960" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_6e42c329-7fcc-4874-87ba-01dffbbea609" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_2e7d0062-f25a-4935-aaec-2b68ae08dcfe" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_2c9fedc8-2b70-421e-b355-3dc222deb960" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_2e7d0062-f25a-4935-aaec-2b68ae08dcfe" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_788ef396-c395-40cb-a879-3cd7785bb958" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_2e7d0062-f25a-4935-aaec-2b68ae08dcfe" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_788ef396-c395-40cb-a879-3cd7785bb958" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/RevenueRemainingPerformanceObligationsDetails_1" xlink:type="simple" xlink:href="sncr-20230930.xsd#RevenueRemainingPerformanceObligationsDetails_1"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/RevenueRemainingPerformanceObligationsDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_2c9fedc8-2b70-421e-b355-3dc222deb960" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_501b31fc-2364-4b78-901a-02f09ba31bd1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_2c9fedc8-2b70-421e-b355-3dc222deb960" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_501b31fc-2364-4b78-901a-02f09ba31bd1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_19681164-6cca-4b4b-8543-d26828123e31" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_2c9fedc8-2b70-421e-b355-3dc222deb960" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_19681164-6cca-4b4b-8543-d26828123e31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_6e42c329-7fcc-4874-87ba-01dffbbea609" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_2c9fedc8-2b70-421e-b355-3dc222deb960" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_6e42c329-7fcc-4874-87ba-01dffbbea609" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_2e7d0062-f25a-4935-aaec-2b68ae08dcfe" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_2c9fedc8-2b70-421e-b355-3dc222deb960" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_2e7d0062-f25a-4935-aaec-2b68ae08dcfe" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/FairValueMeasurementsAssetsandLiabilitiesHeldandtheirRelatedClassificationsUndertheFairValueHierarchyDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#FairValueMeasurementsAssetsandLiabilitiesHeldandtheirRelatedClassificationsUndertheFairValueHierarchyDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/FairValueMeasurementsAssetsandLiabilitiesHeldandtheirRelatedClassificationsUndertheFairValueHierarchyDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_5b7291ba-8bfa-4502-a043-238adc4fc00f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_5a9678d1-acbd-4a8b-bc5b-a2e65b7beb75" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_5b7291ba-8bfa-4502-a043-238adc4fc00f" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_5a9678d1-acbd-4a8b-bc5b-a2e65b7beb75" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_a56e9aeb-76aa-4cfa-938d-3fa18ee47f70" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_5a9678d1-acbd-4a8b-bc5b-a2e65b7beb75" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_a56e9aeb-76aa-4cfa-938d-3fa18ee47f70" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_95c06fb6-37ab-4b5b-bfee-cb718f890d43" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_5a9678d1-acbd-4a8b-bc5b-a2e65b7beb75" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_95c06fb6-37ab-4b5b-bfee-cb718f890d43" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityFairValueDisclosureAbstract_9293ad85-5721-4ba2-aa55-be3f68de5429" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_5b7291ba-8bfa-4502-a043-238adc4fc00f" xlink:to="loc_us-gaap_EquityFairValueDisclosureAbstract_9293ad85-5721-4ba2-aa55-be3f68de5429" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityOtherFairValue_fdf79682-1e4d-4863-96e9-71269e106f51" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RedeemableNoncontrollingInterestEquityOtherFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityFairValueDisclosureAbstract_9293ad85-5721-4ba2-aa55-be3f68de5429" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityOtherFairValue_fdf79682-1e4d-4863-96e9-71269e106f51" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityFairValueDisclosure_76560f59-d868-4f82-b30e-710d96eb704b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityFairValueDisclosureAbstract_9293ad85-5721-4ba2-aa55-be3f68de5429" xlink:to="loc_us-gaap_EquityFairValueDisclosure_76560f59-d868-4f82-b30e-710d96eb704b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_83d6ed88-1a79-402b-bafa-d309ebf52137" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_5b7291ba-8bfa-4502-a043-238adc4fc00f" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_83d6ed88-1a79-402b-bafa-d309ebf52137" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_5418c96c-6c86-4124-8c01-ac10e4bdfb04" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_83d6ed88-1a79-402b-bafa-d309ebf52137" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_5418c96c-6c86-4124-8c01-ac10e4bdfb04" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_5418c96c-6c86-4124-8c01-ac10e4bdfb04_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_5418c96c-6c86-4124-8c01-ac10e4bdfb04" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_5418c96c-6c86-4124-8c01-ac10e4bdfb04_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ebdf1952-72af-4610-ab72-21b41f58a783" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_5418c96c-6c86-4124-8c01-ac10e4bdfb04" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ebdf1952-72af-4610-ab72-21b41f58a783" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_aae1963a-6ee4-4e6d-88ed-2bece1bee6b3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ebdf1952-72af-4610-ab72-21b41f58a783" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_aae1963a-6ee4-4e6d-88ed-2bece1bee6b3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_0b14b133-d285-4b3d-a461-ed290cb17357" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ebdf1952-72af-4610-ab72-21b41f58a783" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_0b14b133-d285-4b3d-a461-ed290cb17357" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_01aa1323-e639-4050-bb34-b9f1809d066e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_ebdf1952-72af-4610-ab72-21b41f58a783" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_01aa1323-e639-4050-bb34-b9f1809d066e" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/LoanReceivableDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#LoanReceivableDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/LoanReceivableDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_33c751b2-c245-4132-b257-ca5f26bba2ce" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_c53f4341-f23b-42f0-aec3-15ded3e40166" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_33c751b2-c245-4132-b257-ca5f26bba2ce" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_c53f4341-f23b-42f0-aec3-15ded3e40166" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentContingentConsiderationLiability_d100a40e-67f6-4692-99a2-48c02c0ceb51" xlink:href="sncr-20230930.xsd#sncr_DebtInstrumentContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_33c751b2-c245-4132-b257-ca5f26bba2ce" xlink:to="loc_sncr_DebtInstrumentContingentConsiderationLiability_d100a40e-67f6-4692-99a2-48c02c0ceb51" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_1d062caf-afc1-4c84-9723-b06157f3069e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_33c751b2-c245-4132-b257-ca5f26bba2ce" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_1d062caf-afc1-4c84-9723-b06157f3069e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsFairValueDisclosure_51d84fc9-b1b6-4e4e-967f-5e5f2e57c58e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherAssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_33c751b2-c245-4132-b257-ca5f26bba2ce" xlink:to="loc_us-gaap_OtherAssetsFairValueDisclosure_51d84fc9-b1b6-4e4e-967f-5e5f2e57c58e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_2b5208c2-4f2c-4d35-808f-b1e84f1e66cc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_33c751b2-c245-4132-b257-ca5f26bba2ce" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_2b5208c2-4f2c-4d35-808f-b1e84f1e66cc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_0ae777cc-c287-4c65-9ccb-6acbb600fc22" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_2b5208c2-4f2c-4d35-808f-b1e84f1e66cc" xlink:to="loc_srt_CounterpartyNameAxis_0ae777cc-c287-4c65-9ccb-6acbb600fc22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_0ae777cc-c287-4c65-9ccb-6acbb600fc22_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_0ae777cc-c287-4c65-9ccb-6acbb600fc22" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_0ae777cc-c287-4c65-9ccb-6acbb600fc22_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_cffcf8bd-f39f-4f46-8eea-7e776a86ae30" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_0ae777cc-c287-4c65-9ccb-6acbb600fc22" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_cffcf8bd-f39f-4f46-8eea-7e776a86ae30" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_SequentialTechnologyInternationalLLCAndAPCapitalHoldingsIILLCMember_27bf63af-81a0-4c32-8fb6-9187d40c2b7a" xlink:href="sncr-20230930.xsd#sncr_SequentialTechnologyInternationalLLCAndAPCapitalHoldingsIILLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_cffcf8bd-f39f-4f46-8eea-7e776a86ae30" xlink:to="loc_sncr_SequentialTechnologyInternationalLLCAndAPCapitalHoldingsIILLCMember_27bf63af-81a0-4c32-8fb6-9187d40c2b7a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_e67913a9-9730-43ab-aaa8-441738a48b61" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_2b5208c2-4f2c-4d35-808f-b1e84f1e66cc" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_e67913a9-9730-43ab-aaa8-441738a48b61" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_e67913a9-9730-43ab-aaa8-441738a48b61_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_e67913a9-9730-43ab-aaa8-441738a48b61" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_e67913a9-9730-43ab-aaa8-441738a48b61_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_927d93af-fd1b-402e-8d69-ea0058bb8656" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_e67913a9-9730-43ab-aaa8-441738a48b61" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_927d93af-fd1b-402e-8d69-ea0058bb8656" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansPayableMember_6c57ed9f-1749-4221-8201-c04bebba9cb0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LoansPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_927d93af-fd1b-402e-8d69-ea0058bb8656" xlink:to="loc_us-gaap_LoansPayableMember_6c57ed9f-1749-4221-8201-c04bebba9cb0" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/DebtOfferingofSeniorNotesDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#DebtOfferingofSeniorNotesDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/DebtOfferingofSeniorNotesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_7e9b462f-6c7e-4342-a42c-1bc81a17e2ef" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_e4f8d6e1-a178-4cf4-86cd-bca9ca249db7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7e9b462f-6c7e-4342-a42c-1bc81a17e2ef" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_e4f8d6e1-a178-4cf4-86cd-bca9ca249db7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_60401da3-8911-422b-aaf1-a9f131ea1c16" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7e9b462f-6c7e-4342-a42c-1bc81a17e2ef" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_60401da3-8911-422b-aaf1-a9f131ea1c16" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentParValue_07b12e64-a369-460f-853c-b6127c138f4b" xlink:href="sncr-20230930.xsd#sncr_DebtInstrumentParValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7e9b462f-6c7e-4342-a42c-1bc81a17e2ef" xlink:to="loc_sncr_DebtInstrumentParValue_07b12e64-a369-460f-853c-b6127c138f4b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentFaceAmountInclusiveOfUnderwritersOptionToPurchase_9a12dc47-356a-4e5b-92d9-6f0d402abe7f" xlink:href="sncr-20230930.xsd#sncr_DebtInstrumentFaceAmountInclusiveOfUnderwritersOptionToPurchase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7e9b462f-6c7e-4342-a42c-1bc81a17e2ef" xlink:to="loc_sncr_DebtInstrumentFaceAmountInclusiveOfUnderwritersOptionToPurchase_9a12dc47-356a-4e5b-92d9-6f0d402abe7f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentUnderwritersOptionToPurchase_ed016c04-bd10-4fd1-b8dc-32d22628a05a" xlink:href="sncr-20230930.xsd#sncr_DebtInstrumentUnderwritersOptionToPurchase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7e9b462f-6c7e-4342-a42c-1bc81a17e2ef" xlink:to="loc_sncr_DebtInstrumentUnderwritersOptionToPurchase_ed016c04-bd10-4fd1-b8dc-32d22628a05a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentRedemptionPrice_e02291d7-603c-4770-bdcf-7fde5e0a1fcc" xlink:href="sncr-20230930.xsd#sncr_DebtInstrumentRedemptionPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7e9b462f-6c7e-4342-a42c-1bc81a17e2ef" xlink:to="loc_sncr_DebtInstrumentRedemptionPrice_e02291d7-603c-4770-bdcf-7fde5e0a1fcc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_6de759d6-403e-495f-bb85-68378ba5de58" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentRedemptionPricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7e9b462f-6c7e-4342-a42c-1bc81a17e2ef" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_6de759d6-403e-495f-bb85-68378ba5de58" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentPercentageOfDebtHoldersDemandFullRepaymentOnDebtDefaultAmount_ca1fe35a-0df7-4adc-a682-b763b71b7466" xlink:href="sncr-20230930.xsd#sncr_DebtInstrumentPercentageOfDebtHoldersDemandFullRepaymentOnDebtDefaultAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7e9b462f-6c7e-4342-a42c-1bc81a17e2ef" xlink:to="loc_sncr_DebtInstrumentPercentageOfDebtHoldersDemandFullRepaymentOnDebtDefaultAmount_ca1fe35a-0df7-4adc-a682-b763b71b7466" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentSalesAgentCompensationPercentage_a45dc97d-eaf4-45c0-90c4-1d1fd5677bf5" xlink:href="sncr-20230930.xsd#sncr_DebtInstrumentSalesAgentCompensationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7e9b462f-6c7e-4342-a42c-1bc81a17e2ef" xlink:to="loc_sncr_DebtInstrumentSalesAgentCompensationPercentage_a45dc97d-eaf4-45c0-90c4-1d1fd5677bf5" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_9eaba19f-6455-4481-b1dd-9d304aadd385" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_7e9b462f-6c7e-4342-a42c-1bc81a17e2ef" xlink:to="loc_us-gaap_DebtInstrumentTable_9eaba19f-6455-4481-b1dd-9d304aadd385" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_d61e4d04-c89b-459c-8c52-efaa2d80c514" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_9eaba19f-6455-4481-b1dd-9d304aadd385" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_d61e4d04-c89b-459c-8c52-efaa2d80c514" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_d61e4d04-c89b-459c-8c52-efaa2d80c514_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_d61e4d04-c89b-459c-8c52-efaa2d80c514" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_d61e4d04-c89b-459c-8c52-efaa2d80c514_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_029dca1c-1fa3-452b-ba12-c3b573a4f324" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_d61e4d04-c89b-459c-8c52-efaa2d80c514" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_029dca1c-1fa3-452b-ba12-c3b573a4f324" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_fb514484-cc32-4414-abc3-b1299b018dba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_029dca1c-1fa3-452b-ba12-c3b573a4f324" xlink:to="loc_us-gaap_SeniorNotesMember_fb514484-cc32-4414-abc3-b1299b018dba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_81d69893-5fcd-416e-9b9b-9b7d06d45311" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_9eaba19f-6455-4481-b1dd-9d304aadd385" xlink:to="loc_us-gaap_DebtInstrumentAxis_81d69893-5fcd-416e-9b9b-9b7d06d45311" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_81d69893-5fcd-416e-9b9b-9b7d06d45311_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_81d69893-5fcd-416e-9b9b-9b7d06d45311" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_81d69893-5fcd-416e-9b9b-9b7d06d45311_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_e24d20d2-4622-4c1a-ae7f-872032cba727" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_81d69893-5fcd-416e-9b9b-9b7d06d45311" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_e24d20d2-4622-4c1a-ae7f-872032cba727" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_SeniorNotesDueJune302026Member_f0e5846c-70f0-4a16-bc9f-cf39214765a6" xlink:href="sncr-20230930.xsd#sncr_SeniorNotesDueJune302026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_e24d20d2-4622-4c1a-ae7f-872032cba727" xlink:to="loc_sncr_SeniorNotesDueJune302026Member_f0e5846c-70f0-4a16-bc9f-cf39214765a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_4f264a66-138f-42c8-96a0-2393e20ac38d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentRedemptionPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_9eaba19f-6455-4481-b1dd-9d304aadd385" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_4f264a66-138f-42c8-96a0-2393e20ac38d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_4f264a66-138f-42c8-96a0-2393e20ac38d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_4f264a66-138f-42c8-96a0-2393e20ac38d" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_4f264a66-138f-42c8-96a0-2393e20ac38d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_f0826707-02d0-4074-97b3-a1d0b8ae1e7c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_4f264a66-138f-42c8-96a0-2393e20ac38d" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_f0826707-02d0-4074-97b3-a1d0b8ae1e7c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_c3ab22ec-427d-4189-abda-63a86372bcc2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentRedemptionPeriodOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_f0826707-02d0-4074-97b3-a1d0b8ae1e7c" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_c3ab22ec-427d-4189-abda-63a86372bcc2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodTwoMember_597f00da-e5a8-48c6-98c3-5d8a8de4d878" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentRedemptionPeriodTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_f0826707-02d0-4074-97b3-a1d0b8ae1e7c" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodTwoMember_597f00da-e5a8-48c6-98c3-5d8a8de4d878" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodThreeMember_8fa47cca-e5db-4fd5-8064-afc702bf3c17" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentRedemptionPeriodThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_f0826707-02d0-4074-97b3-a1d0b8ae1e7c" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodThreeMember_8fa47cca-e5db-4fd5-8064-afc702bf3c17" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/DebtCarryingAmountsDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#DebtCarryingAmountsDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/DebtCarryingAmountsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_17d050be-cf5a-45f9-bc8d-3747badb697b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_aa4737fb-ac26-4ca5-a40c-fb913a5c1f35" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_17d050be-cf5a-45f9-bc8d-3747badb697b" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_aa4737fb-ac26-4ca5-a40c-fb913a5c1f35" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_ed759dc4-9b2e-4c75-95aa-6496a1929a29" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_17d050be-cf5a-45f9-bc8d-3747badb697b" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_ed759dc4-9b2e-4c75-95aa-6496a1929a29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_a4b86578-9165-493a-b4b7-a6faa612c723" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_17d050be-cf5a-45f9-bc8d-3747badb697b" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_a4b86578-9165-493a-b4b7-a6faa612c723" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_d29df799-098d-481e-a237-a963d4ec85a9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_17d050be-cf5a-45f9-bc8d-3747badb697b" xlink:to="loc_us-gaap_LongTermDebt_d29df799-098d-481e-a237-a963d4ec85a9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_b8a037e7-a064-488e-97d3-0a7749d69740" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_17d050be-cf5a-45f9-bc8d-3747badb697b" xlink:to="loc_us-gaap_DebtInstrumentTable_b8a037e7-a064-488e-97d3-0a7749d69740" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_ac4619c7-e76e-4ba5-ba00-467868a9e333" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b8a037e7-a064-488e-97d3-0a7749d69740" xlink:to="loc_us-gaap_DebtInstrumentAxis_ac4619c7-e76e-4ba5-ba00-467868a9e333" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_ac4619c7-e76e-4ba5-ba00-467868a9e333_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_ac4619c7-e76e-4ba5-ba00-467868a9e333" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_ac4619c7-e76e-4ba5-ba00-467868a9e333_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_36eb65ec-eca5-48f1-953d-00dfccdd252e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_ac4619c7-e76e-4ba5-ba00-467868a9e333" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_36eb65ec-eca5-48f1-953d-00dfccdd252e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_SeniorNotesDueJune302026Member_13a34813-4206-4eec-9c78-df55aca404b4" xlink:href="sncr-20230930.xsd#sncr_SeniorNotesDueJune302026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_36eb65ec-eca5-48f1-953d-00dfccdd252e" xlink:to="loc_sncr_SeniorNotesDueJune302026Member_13a34813-4206-4eec-9c78-df55aca404b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_25e92223-40cc-460b-9a21-0168ae1df3fa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b8a037e7-a064-488e-97d3-0a7749d69740" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_25e92223-40cc-460b-9a21-0168ae1df3fa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_25e92223-40cc-460b-9a21-0168ae1df3fa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_25e92223-40cc-460b-9a21-0168ae1df3fa" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_25e92223-40cc-460b-9a21-0168ae1df3fa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_15177f57-d10c-4ca7-bb5c-ac89a7b96332" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_25e92223-40cc-460b-9a21-0168ae1df3fa" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_15177f57-d10c-4ca7-bb5c-ac89a7b96332" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_72372424-44af-43c5-9396-f314287a1097" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_15177f57-d10c-4ca7-bb5c-ac89a7b96332" xlink:to="loc_us-gaap_SeniorNotesMember_72372424-44af-43c5-9396-f314287a1097" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/DebtCarryingValuesandEstimatedFairValuesofDebtInstrumentsDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#DebtCarryingValuesandEstimatedFairValuesofDebtInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/DebtCarryingValuesandEstimatedFairValuesofDebtInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_b785a02f-e483-4123-9604-197b839358ba" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_941f4c4e-293e-4c91-b9a0-c48862a5b635" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_b785a02f-e483-4123-9604-197b839358ba" xlink:to="loc_us-gaap_LongTermDebt_941f4c4e-293e-4c91-b9a0-c48862a5b635" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_5cfb2a0d-4cab-4775-b1f1-8482ce093c9e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_b785a02f-e483-4123-9604-197b839358ba" xlink:to="loc_us-gaap_DebtInstrumentTable_5cfb2a0d-4cab-4775-b1f1-8482ce093c9e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_ffdcb194-4517-42fb-9c7b-e68311c57166" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_5cfb2a0d-4cab-4775-b1f1-8482ce093c9e" xlink:to="loc_us-gaap_DebtInstrumentAxis_ffdcb194-4517-42fb-9c7b-e68311c57166" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_ffdcb194-4517-42fb-9c7b-e68311c57166_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_ffdcb194-4517-42fb-9c7b-e68311c57166" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_ffdcb194-4517-42fb-9c7b-e68311c57166_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_bcf72557-aa01-41c4-adaf-24b75b29bb03" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_ffdcb194-4517-42fb-9c7b-e68311c57166" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_bcf72557-aa01-41c4-adaf-24b75b29bb03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_SeniorNotesDueJune302026Member_7484b635-18bc-41ec-ac04-43959a9cd0ad" xlink:href="sncr-20230930.xsd#sncr_SeniorNotesDueJune302026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_bcf72557-aa01-41c4-adaf-24b75b29bb03" xlink:to="loc_sncr_SeniorNotesDueJune302026Member_7484b635-18bc-41ec-ac04-43959a9cd0ad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_8835d30f-e396-461b-917c-57356694907c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_5cfb2a0d-4cab-4775-b1f1-8482ce093c9e" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_8835d30f-e396-461b-917c-57356694907c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_8835d30f-e396-461b-917c-57356694907c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_8835d30f-e396-461b-917c-57356694907c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_8835d30f-e396-461b-917c-57356694907c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_ce7d369a-d001-441f-8a5c-8a37b94606d7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_8835d30f-e396-461b-917c-57356694907c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_ce7d369a-d001-441f-8a5c-8a37b94606d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_ddffb4ba-59c6-44ad-8993-2371060c28aa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_ce7d369a-d001-441f-8a5c-8a37b94606d7" xlink:to="loc_us-gaap_SeniorNotesMember_ddffb4ba-59c6-44ad-8993-2371060c28aa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_7e4c1803-656c-4d12-b7eb-ac61fd9cfcea" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_5cfb2a0d-4cab-4775-b1f1-8482ce093c9e" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_7e4c1803-656c-4d12-b7eb-ac61fd9cfcea" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7e4c1803-656c-4d12-b7eb-ac61fd9cfcea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_7e4c1803-656c-4d12-b7eb-ac61fd9cfcea" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7e4c1803-656c-4d12-b7eb-ac61fd9cfcea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7d5edb82-ca45-4a90-994f-675aefdc84a5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_7e4c1803-656c-4d12-b7eb-ac61fd9cfcea" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7d5edb82-ca45-4a90-994f-675aefdc84a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_78d93ea8-2e13-4bdf-a402-a2f4e8a3e6a1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7d5edb82-ca45-4a90-994f-675aefdc84a5" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_78d93ea8-2e13-4bdf-a402-a2f4e8a3e6a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_0e6d97a9-6ba2-4bd1-b9c4-84d0ad51368b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7d5edb82-ca45-4a90-994f-675aefdc84a5" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_0e6d97a9-6ba2-4bd1-b9c4-84d0ad51368b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_87997ee6-002d-4c8e-b773-b856af9444bd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7d5edb82-ca45-4a90-994f-675aefdc84a5" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_87997ee6-002d-4c8e-b773-b856af9444bd" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/DebtInterestExpenseDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#DebtInterestExpenseDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/DebtInterestExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_06bece01-d95c-4f5a-9893-95719bd81b10" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_03489f65-cc74-49bb-bcdc-05b616a566e1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_06bece01-d95c-4f5a-9893-95719bd81b10" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_03489f65-cc74-49bb-bcdc-05b616a566e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_aa82080e-a736-4672-9312-34af0dafced8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_06bece01-d95c-4f5a-9893-95719bd81b10" xlink:to="loc_us-gaap_InterestExpenseDebt_aa82080e-a736-4672-9312-34af0dafced8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfDebtDiscountPremium_6826478a-2406-4d32-a0d8-77c9ef71bf1f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AmortizationOfDebtDiscountPremium"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_06bece01-d95c-4f5a-9893-95719bd81b10" xlink:to="loc_us-gaap_AmortizationOfDebtDiscountPremium_6826478a-2406-4d32-a0d8-77c9ef71bf1f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseInterestExpense_9759caea-bbe9-4774-a2be-a90fd9b3cf07" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_FinanceLeaseInterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_06bece01-d95c-4f5a-9893-95719bd81b10" xlink:to="loc_us-gaap_FinanceLeaseInterestExpense_9759caea-bbe9-4774-a2be-a90fd9b3cf07" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseOther_d96d3e32-5282-41cc-9048-4a7d27db61cb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InterestExpenseOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_06bece01-d95c-4f5a-9893-95719bd81b10" xlink:to="loc_us-gaap_InterestExpenseOther_d96d3e32-5282-41cc-9048-4a7d27db61cb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_8bd78b71-49ec-4e5a-b731-6408e6b1bca2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_06bece01-d95c-4f5a-9893-95719bd81b10" xlink:to="loc_us-gaap_InterestExpense_8bd78b71-49ec-4e5a-b731-6408e6b1bca2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_20ea0544-50dd-4dcf-b049-b011570f730f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_06bece01-d95c-4f5a-9893-95719bd81b10" xlink:to="loc_us-gaap_DebtInstrumentTable_20ea0544-50dd-4dcf-b049-b011570f730f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_7c197703-6df8-457c-a173-ca6492799fa7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_20ea0544-50dd-4dcf-b049-b011570f730f" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_7c197703-6df8-457c-a173-ca6492799fa7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_7c197703-6df8-457c-a173-ca6492799fa7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_7c197703-6df8-457c-a173-ca6492799fa7" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_7c197703-6df8-457c-a173-ca6492799fa7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_c5421e63-e596-4120-bc34-d38a0983e82b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_7c197703-6df8-457c-a173-ca6492799fa7" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_c5421e63-e596-4120-bc34-d38a0983e82b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_2256d84a-cea0-466b-b771-b18c0eb5358e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_c5421e63-e596-4120-bc34-d38a0983e82b" xlink:to="loc_us-gaap_SeniorNotesMember_2256d84a-cea0-466b-b771-b18c0eb5358e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_2040cab2-60a5-4f18-9203-759af0dd5a05" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_20ea0544-50dd-4dcf-b049-b011570f730f" xlink:to="loc_us-gaap_DebtInstrumentAxis_2040cab2-60a5-4f18-9203-759af0dd5a05" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_2040cab2-60a5-4f18-9203-759af0dd5a05_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_2040cab2-60a5-4f18-9203-759af0dd5a05" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_2040cab2-60a5-4f18-9203-759af0dd5a05_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_69bc27b9-9d20-426c-8d7f-3a232f894287" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_2040cab2-60a5-4f18-9203-759af0dd5a05" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_69bc27b9-9d20-426c-8d7f-3a232f894287" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_SeniorNotesDueJune302026Member_eaa1dc9e-2473-4fe1-8fb8-a8b0d6177602" xlink:href="sncr-20230930.xsd#sncr_SeniorNotesDueJune302026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_69bc27b9-9d20-426c-8d7f-3a232f894287" xlink:to="loc_sncr_SeniorNotesDueJune302026Member_eaa1dc9e-2473-4fe1-8fb8-a8b0d6177602" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/AccumulatedOtherComprehensiveLossIncomeChangesinAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#AccumulatedOtherComprehensiveLossIncomeChangesinAccumulatedOtherComprehensiveIncomeLossDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/AccumulatedOtherComprehensiveLossIncomeChangesinAccumulatedOtherComprehensiveIncomeLossDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_5c9d8542-0024-4817-a9ff-0b79d9c93ef4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_6ddc8a27-882f-41c5-a468-069394b5b728" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AOCIAttributableToParentNetOfTaxRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_5c9d8542-0024-4817-a9ff-0b79d9c93ef4" xlink:to="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_6ddc8a27-882f-41c5-a468-069394b5b728" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_da39ceec-e6fb-4706-b7e9-2ef70cadea5f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_6ddc8a27-882f-41c5-a468-069394b5b728" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_da39ceec-e6fb-4706-b7e9-2ef70cadea5f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTax_750ebc27-c3e8-491c-a4b4-85ed1663b3e6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_6ddc8a27-882f-41c5-a468-069394b5b728" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTax_750ebc27-c3e8-491c-a4b4-85ed1663b3e6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossTax_ad6017f0-a7fb-46bf-baae-6284632140b9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_OtherComprehensiveIncomeLossTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_6ddc8a27-882f-41c5-a468-069394b5b728" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossTax_ad6017f0-a7fb-46bf-baae-6284632140b9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_3a706dd5-e3e5-4e2b-b3aa-a154a9c7a241" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_26ddb1e7-4403-44e2-b107-51d64d04e794" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_5c9d8542-0024-4817-a9ff-0b79d9c93ef4" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_26ddb1e7-4403-44e2-b107-51d64d04e794" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_d7d2a79a-b885-49f7-a32e-41d9f9dd90ae" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_26ddb1e7-4403-44e2-b107-51d64d04e794" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_d7d2a79a-b885-49f7-a32e-41d9f9dd90ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_d7d2a79a-b885-49f7-a32e-41d9f9dd90ae_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_d7d2a79a-b885-49f7-a32e-41d9f9dd90ae" xlink:to="loc_us-gaap_EquityComponentDomain_d7d2a79a-b885-49f7-a32e-41d9f9dd90ae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_2eceedf5-b067-424b-b586-1d77e3d9830d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_d7d2a79a-b885-49f7-a32e-41d9f9dd90ae" xlink:to="loc_us-gaap_EquityComponentDomain_2eceedf5-b067-424b-b586-1d77e3d9830d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_1cb8cfb6-2ad3-449f-a2e0-e2eeb45e9d9e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_2eceedf5-b067-424b-b586-1d77e3d9830d" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_1cb8cfb6-2ad3-449f-a2e0-e2eeb45e9d9e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_f0dce395-de37-4561-a5f2-38f6242d580e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_1cb8cfb6-2ad3-449f-a2e0-e2eeb45e9d9e" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_f0dce395-de37-4561-a5f2-38f6242d580e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_AccumulatedNetGainLossOnIntraEntityForeignCurrencyTransactionsMember_df10dfc0-118c-40bc-b949-5a671d1a7151" xlink:href="sncr-20230930.xsd#sncr_AccumulatedNetGainLossOnIntraEntityForeignCurrencyTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_1cb8cfb6-2ad3-449f-a2e0-e2eeb45e9d9e" xlink:to="loc_sncr_AccumulatedNetGainLossOnIntraEntityForeignCurrencyTransactionsMember_df10dfc0-118c-40bc-b949-5a671d1a7151" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/CapitalStructureAdditionalInformationDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#CapitalStructureAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CapitalStructureAdditionalInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_NumberOfVotesEachShare_13b0ea1a-6e20-409e-996a-2ddfbbb1ba1b" xlink:href="sncr-20230930.xsd#sncr_NumberOfVotesEachShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_sncr_NumberOfVotesEachShare_13b0ea1a-6e20-409e-996a-2ddfbbb1ba1b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Dividends_156b7fdc-4ec8-4320-92a8-df03c4ab0704" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_Dividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_us-gaap_Dividends_156b7fdc-4ec8-4320-92a8-df03c4ab0704" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_89fe3ba4-0a49-409d-b434-7d35a77104e4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_89fe3ba4-0a49-409d-b434-7d35a77104e4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityParOrStatedValuePerShare_a6094e08-6724-43fe-a6ab-a2f21dc8653a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_us-gaap_TemporaryEquityParOrStatedValuePerShare_a6094e08-6724-43fe-a6ab-a2f21dc8653a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityLiquidationPreferencePerShare_4d9133b6-24f9-4285-b263-1a34efbacfc3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityLiquidationPreferencePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_us-gaap_TemporaryEquityLiquidationPreferencePerShare_4d9133b6-24f9-4285-b263-1a34efbacfc3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_ce9b35c0-1520-4f6f-8993-b2e13ed54f3e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_ce9b35c0-1520-4f6f-8993-b2e13ed54f3e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_PreferredStockDividendRatePercentageOne_740da28e-c19c-4c6c-b403-03c303dc13be" xlink:href="sncr-20230930.xsd#sncr_PreferredStockDividendRatePercentageOne"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_sncr_PreferredStockDividendRatePercentageOne_740da28e-c19c-4c6c-b403-03c303dc13be" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_PreferredStockDividendRatePercentageTwo_da198273-444c-4840-8f16-8a16af12ed15" xlink:href="sncr-20230930.xsd#sncr_PreferredStockDividendRatePercentageTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_sncr_PreferredStockDividendRatePercentageTwo_da198273-444c-4840-8f16-8a16af12ed15" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_PreferredStockDividendRatePercentageThree_dbe948d9-ec1f-46b4-acb1-52837a660b71" xlink:href="sncr-20230930.xsd#sncr_PreferredStockDividendRatePercentageThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_sncr_PreferredStockDividendRatePercentageThree_dbe948d9-ec1f-46b4-acb1-52837a660b71" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityLiquidationValueAndRedemptionValue_2ab61796-5d23-43cd-9137-8e89cf9ad65e" xlink:href="sncr-20230930.xsd#sncr_TemporaryEquityLiquidationValueAndRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_sncr_TemporaryEquityLiquidationValueAndRedemptionValue_2ab61796-5d23-43cd-9137-8e89cf9ad65e" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityRedeemableMultiplierOfPar_6231fa06-63f5-44bd-ade8-e4771117b9c3" xlink:href="sncr-20230930.xsd#sncr_TemporaryEquityRedeemableMultiplierOfPar"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_sncr_TemporaryEquityRedeemableMultiplierOfPar_6231fa06-63f5-44bd-ade8-e4771117b9c3" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentProceedsFromSaleOfStockTransactionsUsedForRedemptionOfShares_e3b483a5-8989-43d7-9b64-1b345621bf8b" xlink:href="sncr-20230930.xsd#sncr_DebtInstrumentProceedsFromSaleOfStockTransactionsUsedForRedemptionOfShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_sncr_DebtInstrumentProceedsFromSaleOfStockTransactionsUsedForRedemptionOfShares_e3b483a5-8989-43d7-9b64-1b345621bf8b" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentProceedsFromSaleOfStockTransactionsUsedForRedemptionOfSharesAndBuyBackOfShares_dc47726e-85bb-4821-94cc-671cd5a10fbd" xlink:href="sncr-20230930.xsd#sncr_DebtInstrumentProceedsFromSaleOfStockTransactionsUsedForRedemptionOfSharesAndBuyBackOfShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_sncr_DebtInstrumentProceedsFromSaleOfStockTransactionsUsedForRedemptionOfSharesAndBuyBackOfShares_dc47726e-85bb-4821-94cc-671cd5a10fbd" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_PreferredStockOwnershipPercentage_4399b8ff-1d92-49df-871c-06a4b3d1b1c6" xlink:href="sncr-20230930.xsd#sncr_PreferredStockOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_sncr_PreferredStockOwnershipPercentage_4399b8ff-1d92-49df-871c-06a4b3d1b1c6" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock_1681397b-9e1d-46fe-89db-f3cc0666b65a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock_1681397b-9e1d-46fe-89db-f3cc0666b65a" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_44519d35-60e4-4d5e-b348-13e4bb6c6279" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_44519d35-60e4-4d5e-b348-13e4bb6c6279" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_3fa5dbec-5863-415c-91ae-498583c8b9e5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_3fa5dbec-5863-415c-91ae-498583c8b9e5" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationShareBasedArrangementsLiabilityCurrent_145d4ba0-23f6-4720-8486-7c7cb07cf1a1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_DeferredCompensationShareBasedArrangementsLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_us-gaap_DeferredCompensationShareBasedArrangementsLiabilityCurrent_145d4ba0-23f6-4720-8486-7c7cb07cf1a1" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_70aff82c-6379-4015-ac3e-ecf8bb9e9a89" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_b9635153-3409-447c-933e-e738d42af6a9" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_70aff82c-6379-4015-ac3e-ecf8bb9e9a89" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_f5e3a078-87b1-4e00-9b7d-a8867abd59b5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_70aff82c-6379-4015-ac3e-ecf8bb9e9a89" xlink:to="loc_us-gaap_StatementClassOfStockAxis_f5e3a078-87b1-4e00-9b7d-a8867abd59b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_f5e3a078-87b1-4e00-9b7d-a8867abd59b5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_f5e3a078-87b1-4e00-9b7d-a8867abd59b5" xlink:to="loc_us-gaap_ClassOfStockDomain_f5e3a078-87b1-4e00-9b7d-a8867abd59b5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_66a71278-3403-41a8-9245-f4b7aee320cf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_f5e3a078-87b1-4e00-9b7d-a8867abd59b5" xlink:to="loc_us-gaap_ClassOfStockDomain_66a71278-3403-41a8-9245-f4b7aee320cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_7753f779-b302-44a4-8253-c694af14ed1c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_66a71278-3403-41a8-9245-f4b7aee320cf" xlink:to="loc_us-gaap_CommonStockMember_7753f779-b302-44a4-8253-c694af14ed1c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesBPreferredStockMember_7994a2bb-d825-403c-8e78-19ac5e5b6fad" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeriesBPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_66a71278-3403-41a8-9245-f4b7aee320cf" xlink:to="loc_us-gaap_SeriesBPreferredStockMember_7994a2bb-d825-403c-8e78-19ac5e5b6fad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_0d872a3a-2878-4c18-98ce-a6b94a7658ae" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_70aff82c-6379-4015-ac3e-ecf8bb9e9a89" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_0d872a3a-2878-4c18-98ce-a6b94a7658ae" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_0d872a3a-2878-4c18-98ce-a6b94a7658ae_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_0d872a3a-2878-4c18-98ce-a6b94a7658ae" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_0d872a3a-2878-4c18-98ce-a6b94a7658ae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_9b3f89fb-f7b5-40cd-aa42-6b891648f90e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_0d872a3a-2878-4c18-98ce-a6b94a7658ae" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_9b3f89fb-f7b5-40cd-aa42-6b891648f90e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrivatePlacementMember_d885a97f-02e1-43ee-9db9-b045ee635d67" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PrivatePlacementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_9b3f89fb-f7b5-40cd-aa42-6b891648f90e" xlink:to="loc_us-gaap_PrivatePlacementMember_d885a97f-02e1-43ee-9db9-b045ee635d67" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_7eda9844-03ae-4bbc-ad98-c59a8dc19374" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_70aff82c-6379-4015-ac3e-ecf8bb9e9a89" xlink:to="loc_us-gaap_PlanNameAxis_7eda9844-03ae-4bbc-ad98-c59a8dc19374" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_7eda9844-03ae-4bbc-ad98-c59a8dc19374_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_7eda9844-03ae-4bbc-ad98-c59a8dc19374" xlink:to="loc_us-gaap_PlanNameDomain_7eda9844-03ae-4bbc-ad98-c59a8dc19374_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_afe4f897-931e-45fa-b4a8-dc396ef9a4ad" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_7eda9844-03ae-4bbc-ad98-c59a8dc19374" xlink:to="loc_us-gaap_PlanNameDomain_afe4f897-931e-45fa-b4a8-dc396ef9a4ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_EquityIncentivePlan2015Member_bf2b0840-6e89-4e35-8a59-21a8d2172789" xlink:href="sncr-20230930.xsd#sncr_EquityIncentivePlan2015Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_afe4f897-931e-45fa-b4a8-dc396ef9a4ad" xlink:to="loc_sncr_EquityIncentivePlan2015Member_bf2b0840-6e89-4e35-8a59-21a8d2172789" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_NewHireEquityIncentivePlan2017Member_bccf4894-258e-4d0f-bfb1-85705c11aecb" xlink:href="sncr-20230930.xsd#sncr_NewHireEquityIncentivePlan2017Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_afe4f897-931e-45fa-b4a8-dc396ef9a4ad" xlink:to="loc_sncr_NewHireEquityIncentivePlan2017Member_bccf4894-258e-4d0f-bfb1-85705c11aecb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_5951c54b-5d71-4988-9481-36ad721e46c9" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_70aff82c-6379-4015-ac3e-ecf8bb9e9a89" xlink:to="loc_srt_RangeAxis_5951c54b-5d71-4988-9481-36ad721e46c9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_5951c54b-5d71-4988-9481-36ad721e46c9_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_5951c54b-5d71-4988-9481-36ad721e46c9" xlink:to="loc_srt_RangeMember_5951c54b-5d71-4988-9481-36ad721e46c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_60edc707-16f4-419f-a488-f51eb198283c" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_5951c54b-5d71-4988-9481-36ad721e46c9" xlink:to="loc_srt_RangeMember_60edc707-16f4-419f-a488-f51eb198283c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_7d62ab40-611c-489a-87c2-fc5b2d856428" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_60edc707-16f4-419f-a488-f51eb198283c" xlink:to="loc_srt_MinimumMember_7d62ab40-611c-489a-87c2-fc5b2d856428" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_425cb00d-cb6b-4477-9b2f-435f78359798" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_60edc707-16f4-419f-a488-f51eb198283c" xlink:to="loc_srt_MaximumMember_425cb00d-cb6b-4477-9b2f-435f78359798" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_5fdb235b-d8fc-407b-a719-2e37aeacdbe7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_70aff82c-6379-4015-ac3e-ecf8bb9e9a89" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_5fdb235b-d8fc-407b-a719-2e37aeacdbe7" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_5fdb235b-d8fc-407b-a719-2e37aeacdbe7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_5fdb235b-d8fc-407b-a719-2e37aeacdbe7" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_5fdb235b-d8fc-407b-a719-2e37aeacdbe7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_76eb4ddb-3602-413a-8277-c641003cff59" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_5fdb235b-d8fc-407b-a719-2e37aeacdbe7" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_76eb4ddb-3602-413a-8277-c641003cff59" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_0c78e753-cd10-401f-887a-a607d848193e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_76eb4ddb-3602-413a-8277-c641003cff59" xlink:to="loc_us-gaap_SubsequentEventMember_0c78e753-cd10-401f-887a-a607d848193e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/CapitalStructurePreferredStockDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#CapitalStructurePreferredStockDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CapitalStructurePreferredStockDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityLineItems_2259b1cc-403c-4c1b-a659-bc6ec1f33695" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_6f5e48bf-f6ad-49f8-8ac4-e1a2da1da5a3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncreaseDecreaseInTemporaryEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_2259b1cc-403c-4c1b-a659-bc6ec1f33695" xlink:to="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_6f5e48bf-f6ad-49f8-8ac4-e1a2da1da5a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_85954c5d-494f-4861-9b27-6d31b2544e0b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_6f5e48bf-f6ad-49f8-8ac4-e1a2da1da5a3" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_85954c5d-494f-4861-9b27-6d31b2544e0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityAmortizationShares_4d6cdf89-059b-422c-ab43-7b784e150f78" xlink:href="sncr-20230930.xsd#sncr_TemporaryEquityAmortizationShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_6f5e48bf-f6ad-49f8-8ac4-e1a2da1da5a3" xlink:to="loc_sncr_TemporaryEquityAmortizationShares_4d6cdf89-059b-422c-ab43-7b784e150f78" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityDividendsShares_49c97608-4d16-49ed-8d63-6ef43bdf0afa" xlink:href="sncr-20230930.xsd#sncr_TemporaryEquityDividendsShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_6f5e48bf-f6ad-49f8-8ac4-e1a2da1da5a3" xlink:to="loc_sncr_TemporaryEquityDividendsShares_49c97608-4d16-49ed-8d63-6ef43bdf0afa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityPreferredStockRedemptionShares_e93573e6-461f-4931-a064-f66a3f8229c5" xlink:href="sncr-20230930.xsd#sncr_TemporaryEquityPreferredStockRedemptionShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_6f5e48bf-f6ad-49f8-8ac4-e1a2da1da5a3" xlink:to="loc_sncr_TemporaryEquityPreferredStockRedemptionShares_e93573e6-461f-4931-a064-f66a3f8229c5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_20e12998-2bc4-41e8-abd8-4366b7bb1679" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests_f87b6c6c-a111-4a23-83bd-def05b780f6f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_6f5e48bf-f6ad-49f8-8ac4-e1a2da1da5a3" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests_f87b6c6c-a111-4a23-83bd-def05b780f6f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityAmortization_15bb4c38-058a-480a-a564-3253da2a476b" xlink:href="sncr-20230930.xsd#sncr_TemporaryEquityAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_6f5e48bf-f6ad-49f8-8ac4-e1a2da1da5a3" xlink:to="loc_sncr_TemporaryEquityAmortization_15bb4c38-058a-480a-a564-3253da2a476b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityDividendsValue_303bcde7-5792-4dd7-9b15-f371450c9428" xlink:href="sncr-20230930.xsd#sncr_TemporaryEquityDividendsValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_6f5e48bf-f6ad-49f8-8ac4-e1a2da1da5a3" xlink:to="loc_sncr_TemporaryEquityDividendsValue_303bcde7-5792-4dd7-9b15-f371450c9428" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityPreferredStockRedemptionValue_d614846f-6ca5-4093-beac-35313029f219" xlink:href="sncr-20230930.xsd#sncr_TemporaryEquityPreferredStockRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_6f5e48bf-f6ad-49f8-8ac4-e1a2da1da5a3" xlink:to="loc_sncr_TemporaryEquityPreferredStockRedemptionValue_d614846f-6ca5-4093-beac-35313029f219" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests_11ed01e1-fff6-45ae-b50c-ac50593c8ed5" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityCarryingAmount_0fc692eb-2c07-4222-b6a1-e861d032d241" xlink:href="sncr-20230930.xsd#sncr_TemporaryEquityCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_2259b1cc-403c-4c1b-a659-bc6ec1f33695" xlink:to="loc_sncr_TemporaryEquityCarryingAmount_0fc692eb-2c07-4222-b6a1-e861d032d241" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityGrossAmount_e7e3ce86-8387-449d-8de1-ee162e93c708" xlink:href="sncr-20230930.xsd#sncr_TemporaryEquityGrossAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_2259b1cc-403c-4c1b-a659-bc6ec1f33695" xlink:to="loc_sncr_TemporaryEquityGrossAmount_e7e3ce86-8387-449d-8de1-ee162e93c708" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityUnamortizedIssuanceCosts_6d9597f1-0e1e-4a0e-97d0-7a2c686bf882" xlink:href="sncr-20230930.xsd#sncr_TemporaryEquityUnamortizedIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_2259b1cc-403c-4c1b-a659-bc6ec1f33695" xlink:to="loc_sncr_TemporaryEquityUnamortizedIssuanceCosts_6d9597f1-0e1e-4a0e-97d0-7a2c686bf882" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c2ea5248-c2df-4f27-92c9-6b400cfe3c84" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TemporaryEquityLineItems_2259b1cc-403c-4c1b-a659-bc6ec1f33695" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c2ea5248-c2df-4f27-92c9-6b400cfe3c84" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_fc6f6800-1129-45e6-87fd-7d0faad796d1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c2ea5248-c2df-4f27-92c9-6b400cfe3c84" xlink:to="loc_us-gaap_StatementClassOfStockAxis_fc6f6800-1129-45e6-87fd-7d0faad796d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_fc6f6800-1129-45e6-87fd-7d0faad796d1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_fc6f6800-1129-45e6-87fd-7d0faad796d1" xlink:to="loc_us-gaap_ClassOfStockDomain_fc6f6800-1129-45e6-87fd-7d0faad796d1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_75b9e0d3-af38-4574-a6de-56de7df52537" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_fc6f6800-1129-45e6-87fd-7d0faad796d1" xlink:to="loc_us-gaap_ClassOfStockDomain_75b9e0d3-af38-4574-a6de-56de7df52537" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesBPreferredStockMember_391db394-1c15-43d0-8b2f-f1d3f31086f1" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SeriesBPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_75b9e0d3-af38-4574-a6de-56de7df52537" xlink:to="loc_us-gaap_SeriesBPreferredStockMember_391db394-1c15-43d0-8b2f-f1d3f31086f1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/CapitalStructureStockbasedCompensationDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#CapitalStructureStockbasedCompensationDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CapitalStructureStockbasedCompensationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1a9e1728-fb02-47c6-adee-c79a1efecd30" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAggregateDisclosuresAbstract_45156ce5-0492-4658-a52d-ce276aa04612" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationAggregateDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1a9e1728-fb02-47c6-adee-c79a1efecd30" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationAggregateDisclosuresAbstract_45156ce5-0492-4658-a52d-ce276aa04612" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_6c7291f0-44d3-40cd-ad16-9cc43713500f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAggregateDisclosuresAbstract_45156ce5-0492-4658-a52d-ce276aa04612" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_6c7291f0-44d3-40cd-ad16-9cc43713500f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_93d68dca-10b6-429b-85dd-fdfd51631036" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAggregateDisclosuresAbstract_45156ce5-0492-4658-a52d-ce276aa04612" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_93d68dca-10b6-429b-85dd-fdfd51631036" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_cbfbaa32-9144-47ae-9fc2-21020058de1a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAggregateDisclosuresAbstract_45156ce5-0492-4658-a52d-ce276aa04612" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_cbfbaa32-9144-47ae-9fc2-21020058de1a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_9f633b5f-37aa-4cc7-85a2-59c096ae957f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAggregateDisclosuresAbstract_45156ce5-0492-4658-a52d-ce276aa04612" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_9f633b5f-37aa-4cc7-85a2-59c096ae957f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_32dc9877-41db-4bc2-b078-e89d289d1381" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1a9e1728-fb02-47c6-adee-c79a1efecd30" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_32dc9877-41db-4bc2-b078-e89d289d1381" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_d29d4088-9c93-4a75-aa4d-45f4cd37f4bc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_32dc9877-41db-4bc2-b078-e89d289d1381" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_d29d4088-9c93-4a75-aa4d-45f4cd37f4bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_d29d4088-9c93-4a75-aa4d-45f4cd37f4bc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_d29d4088-9c93-4a75-aa4d-45f4cd37f4bc" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_d29d4088-9c93-4a75-aa4d-45f4cd37f4bc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_a7c9e7be-0695-439d-9b48-9e80c9591408" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_d29d4088-9c93-4a75-aa4d-45f4cd37f4bc" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_a7c9e7be-0695-439d-9b48-9e80c9591408" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_b69b850b-ac8f-4102-a258-45cb1e4b13b9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_a7c9e7be-0695-439d-9b48-9e80c9591408" xlink:to="loc_us-gaap_CostOfSalesMember_b69b850b-ac8f-4102-a258-45cb1e4b13b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_ed1c5e01-3923-4dfb-9e86-18cfab4c4eca" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_a7c9e7be-0695-439d-9b48-9e80c9591408" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_ed1c5e01-3923-4dfb-9e86-18cfab4c4eca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_ddf7c391-9272-4042-aea9-736cc7f6508a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_a7c9e7be-0695-439d-9b48-9e80c9591408" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_ddf7c391-9272-4042-aea9-736cc7f6508a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_12955e58-8621-4bcd-8e3c-ed036fd6bdb6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_32dc9877-41db-4bc2-b078-e89d289d1381" xlink:to="loc_us-gaap_AwardTypeAxis_12955e58-8621-4bcd-8e3c-ed036fd6bdb6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_12955e58-8621-4bcd-8e3c-ed036fd6bdb6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_12955e58-8621-4bcd-8e3c-ed036fd6bdb6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_12955e58-8621-4bcd-8e3c-ed036fd6bdb6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a419d294-965f-4514-8e80-43d53ebf0bcb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_12955e58-8621-4bcd-8e3c-ed036fd6bdb6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a419d294-965f-4514-8e80-43d53ebf0bcb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_EmployeeAndDirectorsStockOptionsMember_86f69c26-419b-4735-97b2-f5c2bb766797" xlink:href="sncr-20230930.xsd#sncr_EmployeeAndDirectorsStockOptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a419d294-965f-4514-8e80-43d53ebf0bcb" xlink:to="loc_sncr_EmployeeAndDirectorsStockOptionsMember_86f69c26-419b-4735-97b2-f5c2bb766797" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_094fbd42-b66b-4390-bf29-c39fec902623" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a419d294-965f-4514-8e80-43d53ebf0bcb" xlink:to="loc_us-gaap_RestrictedStockMember_094fbd42-b66b-4390-bf29-c39fec902623" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_32a8efc0-4718-4dab-99c9-24ed758be657" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a419d294-965f-4514-8e80-43d53ebf0bcb" xlink:to="loc_us-gaap_PerformanceSharesMember_32a8efc0-4718-4dab-99c9-24ed758be657" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/CapitalStructureBlackScholesAssumptionsDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#CapitalStructureBlackScholesAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CapitalStructureBlackScholesAssumptionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1e7c8aa9-c83f-4988-a540-9f00a3d5d06d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_159b79a3-6a22-4323-8fd8-e2461c610864" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1e7c8aa9-c83f-4988-a540-9f00a3d5d06d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_159b79a3-6a22-4323-8fd8-e2461c610864" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_86a04a82-7793-45ea-a9c0-323885075b1e" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_159b79a3-6a22-4323-8fd8-e2461c610864" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_86a04a82-7793-45ea-a9c0-323885075b1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_dc66d229-cb27-454b-8e60-52e87e95ef71" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_159b79a3-6a22-4323-8fd8-e2461c610864" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_dc66d229-cb27-454b-8e60-52e87e95ef71" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_4b6b2050-160d-4614-8a8e-d7fc29bf909d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_159b79a3-6a22-4323-8fd8-e2461c610864" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_4b6b2050-160d-4614-8a8e-d7fc29bf909d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_4f22380a-09a5-495b-be16-cce492143f20" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_159b79a3-6a22-4323-8fd8-e2461c610864" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_4f22380a-09a5-495b-be16-cce492143f20" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_c7b4b223-db95-40e2-9c98-b2b00efa9cc2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_159b79a3-6a22-4323-8fd8-e2461c610864" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_c7b4b223-db95-40e2-9c98-b2b00efa9cc2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_98ceed93-1be8-4f67-a68f-d21414a439ae" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1e7c8aa9-c83f-4988-a540-9f00a3d5d06d" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_98ceed93-1be8-4f67-a68f-d21414a439ae" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_c87bc846-7c51-432d-92d9-c1ee9e59ec8f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_98ceed93-1be8-4f67-a68f-d21414a439ae" xlink:to="loc_us-gaap_AwardTypeAxis_c87bc846-7c51-432d-92d9-c1ee9e59ec8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c87bc846-7c51-432d-92d9-c1ee9e59ec8f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_c87bc846-7c51-432d-92d9-c1ee9e59ec8f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c87bc846-7c51-432d-92d9-c1ee9e59ec8f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7ca660fd-eb81-4898-ad19-97a3c837b369" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_c87bc846-7c51-432d-92d9-c1ee9e59ec8f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7ca660fd-eb81-4898-ad19-97a3c837b369" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_EmployeeAndDirectorsStockOptionsMember_805f7d41-7d86-46ed-b601-97b9efd48e5c" xlink:href="sncr-20230930.xsd#sncr_EmployeeAndDirectorsStockOptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_7ca660fd-eb81-4898-ad19-97a3c837b369" xlink:to="loc_sncr_EmployeeAndDirectorsStockOptionsMember_805f7d41-7d86-46ed-b601-97b9efd48e5c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/CapitalStructureRestrictedStockDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#CapitalStructureRestrictedStockDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CapitalStructureRestrictedStockDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b18300a5-311d-4dea-a318-fb29499a7fa7" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_51e05538-6bd7-4b9b-812e-bf1de8912189" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b18300a5-311d-4dea-a318-fb29499a7fa7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_51e05538-6bd7-4b9b-812e-bf1de8912189" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_ce2b855b-4e5c-4949-85e6-975de8eba825" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_51e05538-6bd7-4b9b-812e-bf1de8912189" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_ce2b855b-4e5c-4949-85e6-975de8eba825" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_f5dba1e9-2ad4-4cc5-b8e5-e6438ef1b0fd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_51e05538-6bd7-4b9b-812e-bf1de8912189" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_f5dba1e9-2ad4-4cc5-b8e5-e6438ef1b0fd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsAdjustmentInPeriod_91789d23-a647-4455-9fe0-31c9a4698c4c" xlink:href="sncr-20230930.xsd#sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsAdjustmentInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_51e05538-6bd7-4b9b-812e-bf1de8912189" xlink:to="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsAdjustmentInPeriod_91789d23-a647-4455-9fe0-31c9a4698c4c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_3537cfc8-a643-421f-8444-a1f42aa61fed" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_51e05538-6bd7-4b9b-812e-bf1de8912189" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_3537cfc8-a643-421f-8444-a1f42aa61fed" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_b6a2ff95-27dd-4c94-84ea-7469b13b9d35" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_51e05538-6bd7-4b9b-812e-bf1de8912189" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_b6a2ff95-27dd-4c94-84ea-7469b13b9d35" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_5e43f2f0-3815-4883-aaf6-5bb00eec4eee" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_4aa59502-adc5-4e76-97cc-9fcefbe89459" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b18300a5-311d-4dea-a318-fb29499a7fa7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_4aa59502-adc5-4e76-97cc-9fcefbe89459" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_affdde18-1e3f-436b-9d28-cf3803214c57" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_4aa59502-adc5-4e76-97cc-9fcefbe89459" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_affdde18-1e3f-436b-9d28-cf3803214c57" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_bcc8d2ab-2192-4445-9b61-d49ece2b8979" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_4aa59502-adc5-4e76-97cc-9fcefbe89459" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_bcc8d2ab-2192-4445-9b61-d49ece2b8979" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsAdjustmentInPeriodWeightedAverageGrantDateFairValue_7ec13e7d-2bf4-4e63-be54-f5aeac7cc053" xlink:href="sncr-20230930.xsd#sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsAdjustmentInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_4aa59502-adc5-4e76-97cc-9fcefbe89459" xlink:to="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsAdjustmentInPeriodWeightedAverageGrantDateFairValue_7ec13e7d-2bf4-4e63-be54-f5aeac7cc053" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_845661fc-a9c9-4d1d-ab19-05c51165a5ac" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_4aa59502-adc5-4e76-97cc-9fcefbe89459" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_845661fc-a9c9-4d1d-ab19-05c51165a5ac" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_f5aeaa85-363e-4626-8c3d-5c417d2baa2c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_4aa59502-adc5-4e76-97cc-9fcefbe89459" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_f5aeaa85-363e-4626-8c3d-5c417d2baa2c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_e4bcc353-8001-46cb-a2e3-77e19505d793" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_4e5d8c56-b2fd-4870-aa24-3e857fa37fea" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b18300a5-311d-4dea-a318-fb29499a7fa7" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_4e5d8c56-b2fd-4870-aa24-3e857fa37fea" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_91be27f3-0715-4d40-8b98-3a418fa06a96" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_4e5d8c56-b2fd-4870-aa24-3e857fa37fea" xlink:to="loc_us-gaap_AwardTypeAxis_91be27f3-0715-4d40-8b98-3a418fa06a96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_91be27f3-0715-4d40-8b98-3a418fa06a96_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_91be27f3-0715-4d40-8b98-3a418fa06a96" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_91be27f3-0715-4d40-8b98-3a418fa06a96_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a0564359-1a3b-4b9c-8f60-d720922440c3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_91be27f3-0715-4d40-8b98-3a418fa06a96" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a0564359-1a3b-4b9c-8f60-d720922440c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_a98a2ba1-f877-4e42-a928-6f4b98cfba39" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a0564359-1a3b-4b9c-8f60-d720922440c3" xlink:to="loc_us-gaap_RestrictedStockMember_a98a2ba1-f877-4e42-a928-6f4b98cfba39" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_e1fa5837-178b-4b10-a9ee-50e8103d3845" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a0564359-1a3b-4b9c-8f60-d720922440c3" xlink:to="loc_us-gaap_PerformanceSharesMember_e1fa5837-178b-4b10-a9ee-50e8103d3845" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/CapitalStructurePerformanceStockDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#CapitalStructurePerformanceStockDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CapitalStructurePerformanceStockDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4efa150c-e25a-4e5e-876c-5e22cebf931f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_7987834a-9841-45c0-978b-e8ff846cba93" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4efa150c-e25a-4e5e-876c-5e22cebf931f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_7987834a-9841-45c0-978b-e8ff846cba93" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_de7b0dbf-cdd2-4d1a-8ef4-f0db201922a4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4efa150c-e25a-4e5e-876c-5e22cebf931f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_de7b0dbf-cdd2-4d1a-8ef4-f0db201922a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_0c09c60f-e2be-4f50-ac7b-beaf8b7018bf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_de7b0dbf-cdd2-4d1a-8ef4-f0db201922a4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_0c09c60f-e2be-4f50-ac7b-beaf8b7018bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_0b4451b4-36c8-44da-a182-33977862f6ff" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_de7b0dbf-cdd2-4d1a-8ef4-f0db201922a4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGranted_0b4451b4-36c8-44da-a182-33977862f6ff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedAdjustmentInPeriod_aaf30477-0c31-46ec-b18a-923f941d55e2" xlink:href="sncr-20230930.xsd#sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedAdjustmentInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_de7b0dbf-cdd2-4d1a-8ef4-f0db201922a4" xlink:to="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedAdjustmentInPeriod_aaf30477-0c31-46ec-b18a-923f941d55e2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityIntrumentsVestedAndDistributedInPeriod_6ba9cf3c-3158-4e02-883e-4524084d1d67" xlink:href="sncr-20230930.xsd#sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityIntrumentsVestedAndDistributedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_de7b0dbf-cdd2-4d1a-8ef4-f0db201922a4" xlink:to="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityIntrumentsVestedAndDistributedInPeriod_6ba9cf3c-3158-4e02-883e-4524084d1d67" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeitures_2c1ce878-f703-42c9-a0a8-52e0c133eec8" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingRollForward_de7b0dbf-cdd2-4d1a-8ef4-f0db201922a4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeitures_2c1ce878-f703-42c9-a0a8-52e0c133eec8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber_088595ae-ba59-4808-bad5-f38015fe5824" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_700f9f30-77a9-4c37-b42b-1c6495eab830" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4efa150c-e25a-4e5e-876c-5e22cebf931f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_700f9f30-77a9-4c37-b42b-1c6495eab830" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageGrantDateFairValue_aff5db12-e8f5-490d-a72f-c45f9072f774" xlink:href="sncr-20230930.xsd#sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_700f9f30-77a9-4c37-b42b-1c6495eab830" xlink:to="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageGrantDateFairValue_aff5db12-e8f5-490d-a72f-c45f9072f774" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedWeightedAverageGrantDateFairValue_04218089-da65-4975-9687-782162dea484" xlink:href="sncr-20230930.xsd#sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_700f9f30-77a9-4c37-b42b-1c6495eab830" xlink:to="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedWeightedAverageGrantDateFairValue_04218089-da65-4975-9687-782162dea484" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedAdjustmentInPeriodWeightedAverageGrantDateFairValue_df0761a4-74c3-43a1-9ffb-a485cb9adb57" xlink:href="sncr-20230930.xsd#sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedAdjustmentInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_700f9f30-77a9-4c37-b42b-1c6495eab830" xlink:to="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsGrantedAdjustmentInPeriodWeightedAverageGrantDateFairValue_df0761a4-74c3-43a1-9ffb-a485cb9adb57" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedAndDistributedInPeriodWeightedAverageExercisePrice_72c91004-a064-4b0c-90bf-76cbeebf767f" xlink:href="sncr-20230930.xsd#sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedAndDistributedInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_700f9f30-77a9-4c37-b42b-1c6495eab830" xlink:to="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsVestedAndDistributedInPeriodWeightedAverageExercisePrice_72c91004-a064-4b0c-90bf-76cbeebf767f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresWeightedAverageGrantDateFairValue_d25dddec-7a3c-410d-834e-46231c8ae99f" xlink:href="sncr-20230930.xsd#sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_700f9f30-77a9-4c37-b42b-1c6495eab830" xlink:to="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsForfeituresWeightedAverageGrantDateFairValue_d25dddec-7a3c-410d-834e-46231c8ae99f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageGrantDateFairValue_d744d6ad-4e52-4fe5-9e8f-7fbcd1fad1bb" xlink:href="sncr-20230930.xsd#sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_501f45e9-1984-4b55-909d-404ec027e25a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_4efa150c-e25a-4e5e-876c-5e22cebf931f" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_501f45e9-1984-4b55-909d-404ec027e25a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_e90b97d0-0b2a-487a-b849-2e1882d1aafd" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_501f45e9-1984-4b55-909d-404ec027e25a" xlink:to="loc_us-gaap_AwardTypeAxis_e90b97d0-0b2a-487a-b849-2e1882d1aafd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e90b97d0-0b2a-487a-b849-2e1882d1aafd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_e90b97d0-0b2a-487a-b849-2e1882d1aafd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e90b97d0-0b2a-487a-b849-2e1882d1aafd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e5b52d1f-4e1d-487b-b27f-4e7b232fedfa" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_e90b97d0-0b2a-487a-b849-2e1882d1aafd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e5b52d1f-4e1d-487b-b27f-4e7b232fedfa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_3a80ca18-7539-486a-925e-e929e2080d19" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e5b52d1f-4e1d-487b-b27f-4e7b232fedfa" xlink:to="loc_us-gaap_PerformanceSharesMember_3a80ca18-7539-486a-925e-e929e2080d19" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_d272f0f1-d12c-41ab-8e58-e3a71d4c1336" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_501f45e9-1984-4b55-909d-404ec027e25a" xlink:to="loc_us-gaap_PlanNameAxis_d272f0f1-d12c-41ab-8e58-e3a71d4c1336" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_d272f0f1-d12c-41ab-8e58-e3a71d4c1336_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_d272f0f1-d12c-41ab-8e58-e3a71d4c1336" xlink:to="loc_us-gaap_PlanNameDomain_d272f0f1-d12c-41ab-8e58-e3a71d4c1336_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_a9f73443-19a1-4726-aed0-f4e59fb55dbf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_d272f0f1-d12c-41ab-8e58-e3a71d4c1336" xlink:to="loc_us-gaap_PlanNameDomain_a9f73443-19a1-4726-aed0-f4e59fb55dbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_EquityIncentivePlan2015Member_e241d746-f950-4fb8-af70-b778c418ff27" xlink:href="sncr-20230930.xsd#sncr_EquityIncentivePlan2015Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_a9f73443-19a1-4726-aed0-f4e59fb55dbf" xlink:to="loc_sncr_EquityIncentivePlan2015Member_e241d746-f950-4fb8-af70-b778c418ff27" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/RestructuringRestructuringAccrualandChangesDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#RestructuringRestructuringAccrualandChangesDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/RestructuringRestructuringAccrualandChangesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_daa57266-58ed-47e7-870a-aabb50f217cf" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveRollForward_ff4b6f3e-d980-4be3-a3c9-d89f344184f0" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringReserveRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_daa57266-58ed-47e7-870a-aabb50f217cf" xlink:to="loc_us-gaap_RestructuringReserveRollForward_ff4b6f3e-d980-4be3-a3c9-d89f344184f0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_079fa942-944a-42fa-8bfa-fa038953b93a" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_ff4b6f3e-d980-4be3-a3c9-d89f344184f0" xlink:to="loc_us-gaap_RestructuringReserve_079fa942-944a-42fa-8bfa-fa038953b93a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_4534c5e5-2ced-4059-bd05-a370edd089c9" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_ff4b6f3e-d980-4be3-a3c9-d89f344184f0" xlink:to="loc_us-gaap_RestructuringCharges_4534c5e5-2ced-4059-bd05-a370edd089c9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRestructuring_6fdd6551-63a0-4297-a6a2-9c2e814c04d6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PaymentsForRestructuring"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_ff4b6f3e-d980-4be3-a3c9-d89f344184f0" xlink:to="loc_us-gaap_PaymentsForRestructuring_6fdd6551-63a0-4297-a6a2-9c2e814c04d6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveTranslationAndOtherAdjustment_07fa6221-27c8-4e6a-9598-9e1929d9d28b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringReserveTranslationAndOtherAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_ff4b6f3e-d980-4be3-a3c9-d89f344184f0" xlink:to="loc_us-gaap_RestructuringReserveTranslationAndOtherAdjustment_07fa6221-27c8-4e6a-9598-9e1929d9d28b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_ba2a8aad-51d9-42be-9441-97e0bac268ea" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringReserve"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_469507e0-5984-4998-81d4-b4922dc7b9ea" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_daa57266-58ed-47e7-870a-aabb50f217cf" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_469507e0-5984-4998-81d4-b4922dc7b9ea" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_98d68af2-02b3-4884-be8a-58f534accb06" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_469507e0-5984-4998-81d4-b4922dc7b9ea" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_98d68af2-02b3-4884-be8a-58f534accb06" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_98d68af2-02b3-4884-be8a-58f534accb06_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_98d68af2-02b3-4884-be8a-58f534accb06" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_98d68af2-02b3-4884-be8a-58f534accb06_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_2940ddcf-5bfe-4e72-8eae-e680805a36eb" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_98d68af2-02b3-4884-be8a-58f534accb06" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_2940ddcf-5bfe-4e72-8eae-e680805a36eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_4ac24a73-cea2-4aa5-b9c6-abeabdd1b167" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_2940ddcf-5bfe-4e72-8eae-e680805a36eb" xlink:to="loc_us-gaap_EmployeeSeveranceMember_4ac24a73-cea2-4aa5-b9c6-abeabdd1b167" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/EarningsperCommonShareEPSReconciliationoftheNumeratorandDenominatorUsedinComputingBasicandDilutedNetIncomeAttributabletoCommonStockholdersPerCommonShareDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#EarningsperCommonShareEPSReconciliationoftheNumeratorandDenominatorUsedinComputingBasicandDilutedNetIncomeAttributabletoCommonStockholdersPerCommonShareDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/EarningsperCommonShareEPSReconciliationoftheNumeratorandDenominatorUsedinComputingBasicandDilutedNetIncomeAttributabletoCommonStockholdersPerCommonShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasicLineItems_d1e2f852-c0ea-447a-89c3-6f34a4f8ef44" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EarningsPerShareBasicLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareReconciliationAbstract_16df8c0a-8e5d-4477-9ad2-5119d2cf9d92" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EarningsPerShareReconciliationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_d1e2f852-c0ea-447a-89c3-6f34a4f8ef44" xlink:to="loc_us-gaap_EarningsPerShareReconciliationAbstract_16df8c0a-8e5d-4477-9ad2-5119d2cf9d92" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest_bbcde280-a29c-4158-baf8-9d6426550548" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareReconciliationAbstract_16df8c0a-8e5d-4477-9ad2-5119d2cf9d92" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest_bbcde280-a29c-4158-baf8-9d6426550548" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_712d5839-91f4-42d2-a08d-374d585f0a13" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareReconciliationAbstract_16df8c0a-8e5d-4477-9ad2-5119d2cf9d92" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_712d5839-91f4-42d2-a08d-374d585f0a13" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockDividendsAndOtherAdjustments_36aa88df-d967-4d09-aa93-ebd9862dba77" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_PreferredStockDividendsAndOtherAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareReconciliationAbstract_16df8c0a-8e5d-4477-9ad2-5119d2cf9d92" xlink:to="loc_us-gaap_PreferredStockDividendsAndOtherAdjustments_36aa88df-d967-4d09-aa93-ebd9862dba77" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_1d0b80e8-713d-4507-83f8-c113a633bfc2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareReconciliationAbstract_16df8c0a-8e5d-4477-9ad2-5119d2cf9d92" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_1d0b80e8-713d-4507-83f8-c113a633bfc2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperations_bfee2893-e3b1-444e-82e6-96b4e72acfd2" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_IncomeLossFromContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareReconciliationAbstract_16df8c0a-8e5d-4477-9ad2-5119d2cf9d92" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperations_bfee2893-e3b1-444e-82e6-96b4e72acfd2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_feebd0e7-fb73-47b1-8f28-536a4e1704a6" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareReconciliationAbstract_16df8c0a-8e5d-4477-9ad2-5119d2cf9d92" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_feebd0e7-fb73-47b1-8f28-536a4e1704a6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_3c6e0d5b-472c-4dcc-8d76-31adddaa506c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_feebd0e7-fb73-47b1-8f28-536a4e1704a6" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_3c6e0d5b-472c-4dcc-8d76-31adddaa506c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_36c26929-87e1-4816-90a9-c180eaeec828" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_feebd0e7-fb73-47b1-8f28-536a4e1704a6" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_36c26929-87e1-4816-90a9-c180eaeec828" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasicAbstract_f3b72415-0efb-43d9-ac49-2cd256d45c4c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EarningsPerShareBasicAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareReconciliationAbstract_16df8c0a-8e5d-4477-9ad2-5119d2cf9d92" xlink:to="loc_us-gaap_EarningsPerShareBasicAbstract_f3b72415-0efb-43d9-ac49-2cd256d45c4c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_7435194e-bc98-44ee-8199-6d7cbc38c24c" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_f3b72415-0efb-43d9-ac49-2cd256d45c4c" xlink:to="loc_us-gaap_EarningsPerShareBasic_7435194e-bc98-44ee-8199-6d7cbc38c24c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_7f8b10a3-0008-4045-a7f5-b58da1bcc43f" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_f3b72415-0efb-43d9-ac49-2cd256d45c4c" xlink:to="loc_us-gaap_EarningsPerShareDiluted_7f8b10a3-0008-4045-a7f5-b58da1bcc43f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_dbcfb90b-a3bc-4674-9df6-d234439d47f3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_d1e2f852-c0ea-447a-89c3-6f34a4f8ef44" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_dbcfb90b-a3bc-4674-9df6-d234439d47f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_009a0ffc-2871-4f68-bbc3-31188f651777" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_d1e2f852-c0ea-447a-89c3-6f34a4f8ef44" xlink:to="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_009a0ffc-2871-4f68-bbc3-31188f651777" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_e90caf03-a6bf-446e-aa5b-d423fc0c1e7d" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_009a0ffc-2871-4f68-bbc3-31188f651777" xlink:to="loc_us-gaap_AwardTypeAxis_e90caf03-a6bf-446e-aa5b-d423fc0c1e7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e90caf03-a6bf-446e-aa5b-d423fc0c1e7d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_e90caf03-a6bf-446e-aa5b-d423fc0c1e7d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e90caf03-a6bf-446e-aa5b-d423fc0c1e7d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e951943d-5a45-4828-bef4-8697c3bf127b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_e90caf03-a6bf-446e-aa5b-d423fc0c1e7d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e951943d-5a45-4828-bef4-8697c3bf127b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_1b2bfb52-a72d-416b-936a-bb3cd5dcd0cc" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_e951943d-5a45-4828-bef4-8697c3bf127b" xlink:to="loc_us-gaap_RestrictedStockMember_1b2bfb52-a72d-416b-936a-bb3cd5dcd0cc" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="sncr-20230930.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_e54e2dfd-7cd2-4ba6-88ef-20b1d543c7f3" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionConsiderationTransferred_bcbc5da2-effb-4c98-aab7-e45f748cbc93" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetAcquisitionConsiderationTransferred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e54e2dfd-7cd2-4ba6-88ef-20b1d543c7f3" xlink:to="loc_us-gaap_AssetAcquisitionConsiderationTransferred_bcbc5da2-effb-4c98-aab7-e45f748cbc93" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_PaymentsForAssetAcquisitions_de52cb1d-6b10-4531-a430-7550d72bb8aa" xlink:href="sncr-20230930.xsd#sncr_PaymentsForAssetAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e54e2dfd-7cd2-4ba6-88ef-20b1d543c7f3" xlink:to="loc_sncr_PaymentsForAssetAcquisitions_de52cb1d-6b10-4531-a430-7550d72bb8aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EscrowDeposit_854e198d-8285-4f2f-a20f-665915f1cd7b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_EscrowDeposit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e54e2dfd-7cd2-4ba6-88ef-20b1d543c7f3" xlink:to="loc_us-gaap_EscrowDeposit_854e198d-8285-4f2f-a20f-665915f1cd7b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_PeriodOfDaysFollowingClosingDate_3e76e845-1f52-4ec3-bd1f-935ac305860b" xlink:href="sncr-20230930.xsd#sncr_PeriodOfDaysFollowingClosingDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e54e2dfd-7cd2-4ba6-88ef-20b1d543c7f3" xlink:to="loc_sncr_PeriodOfDaysFollowingClosingDate_3e76e845-1f52-4ec3-bd1f-935ac305860b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_EscrowDepositAdditionalAmount_57eb076a-4c6c-4084-b02a-0e55ea5eea72" xlink:href="sncr-20230930.xsd#sncr_EscrowDepositAdditionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e54e2dfd-7cd2-4ba6-88ef-20b1d543c7f3" xlink:to="loc_sncr_EscrowDepositAdditionalAmount_57eb076a-4c6c-4084-b02a-0e55ea5eea72" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_EscrowDepositCashAdditionalAmount_8d818ca8-6225-42b2-aa5b-5ce920174721" xlink:href="sncr-20230930.xsd#sncr_EscrowDepositCashAdditionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e54e2dfd-7cd2-4ba6-88ef-20b1d543c7f3" xlink:to="loc_sncr_EscrowDepositCashAdditionalAmount_8d818ca8-6225-42b2-aa5b-5ce920174721" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_AssetAcquisitionConsiderationTransferredEquityInterestsIssuedAndReedemedShares_7b0c994c-dd3c-4818-a785-42fe6dabc46d" xlink:href="sncr-20230930.xsd#sncr_AssetAcquisitionConsiderationTransferredEquityInterestsIssuedAndReedemedShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e54e2dfd-7cd2-4ba6-88ef-20b1d543c7f3" xlink:to="loc_sncr_AssetAcquisitionConsiderationTransferredEquityInterestsIssuedAndReedemedShares_7b0c994c-dd3c-4818-a785-42fe6dabc46d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ProceedsFromAccountsReceivableFacility_2e15d4c6-7a18-4538-a3f8-576f5f168881" xlink:href="sncr-20230930.xsd#sncr_ProceedsFromAccountsReceivableFacility"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_e54e2dfd-7cd2-4ba6-88ef-20b1d543c7f3" xlink:to="loc_sncr_ProceedsFromAccountsReceivableFacility_2e15d4c6-7a18-4538-a3f8-576f5f168881" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_19ff802e-d688-4017-95b5-719d26ad4cde" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_e54e2dfd-7cd2-4ba6-88ef-20b1d543c7f3" xlink:to="loc_us-gaap_SubsequentEventTable_19ff802e-d688-4017-95b5-719d26ad4cde" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_0f45ac1f-9ba8-49d8-be4f-caedfa244202" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_19ff802e-d688-4017-95b5-719d26ad4cde" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_0f45ac1f-9ba8-49d8-be4f-caedfa244202" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_0f45ac1f-9ba8-49d8-be4f-caedfa244202_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_0f45ac1f-9ba8-49d8-be4f-caedfa244202" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_0f45ac1f-9ba8-49d8-be4f-caedfa244202_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_3d664467-7a68-4f21-81d4-1e99954179b4" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_0f45ac1f-9ba8-49d8-be4f-caedfa244202" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_3d664467-7a68-4f21-81d4-1e99954179b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_ec10a492-8305-489d-a67c-3b258559b94b" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_3d664467-7a68-4f21-81d4-1e99954179b4" xlink:to="loc_us-gaap_SubsequentEventMember_ec10a492-8305-489d-a67c-3b258559b94b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionAxis_c91a1429-703b-4a5e-80b0-f16f6ade75da" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_19ff802e-d688-4017-95b5-719d26ad4cde" xlink:to="loc_us-gaap_AssetAcquisitionAxis_c91a1429-703b-4a5e-80b0-f16f6ade75da" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_c91a1429-703b-4a5e-80b0-f16f6ade75da_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AssetAcquisitionAxis_c91a1429-703b-4a5e-80b0-f16f6ade75da" xlink:to="loc_us-gaap_AssetAcquisitionDomain_c91a1429-703b-4a5e-80b0-f16f6ade75da_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetAcquisitionDomain_d61bfc38-e549-41c8-8569-6d779ac7e757" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AssetAcquisitionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AssetAcquisitionAxis_c91a1429-703b-4a5e-80b0-f16f6ade75da" xlink:to="loc_us-gaap_AssetAcquisitionDomain_d61bfc38-e549-41c8-8569-6d779ac7e757" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_MessagingAndDigitalBusinessesMember_c9800f69-ce49-49b5-8e68-ae0cb881feeb" xlink:href="sncr-20230930.xsd#sncr_MessagingAndDigitalBusinessesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetAcquisitionDomain_d61bfc38-e549-41c8-8569-6d779ac7e757" xlink:to="loc_sncr_MessagingAndDigitalBusinessesMember_c9800f69-ce49-49b5-8e68-ae0cb881feeb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_060ce5f2-d7cc-431e-bb10-4da15d803a82" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_19ff802e-d688-4017-95b5-719d26ad4cde" xlink:to="loc_us-gaap_StatementClassOfStockAxis_060ce5f2-d7cc-431e-bb10-4da15d803a82" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_060ce5f2-d7cc-431e-bb10-4da15d803a82_default" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_060ce5f2-d7cc-431e-bb10-4da15d803a82" xlink:to="loc_us-gaap_ClassOfStockDomain_060ce5f2-d7cc-431e-bb10-4da15d803a82_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_020c529d-c0fd-445f-95d0-753643924d71" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_060ce5f2-d7cc-431e-bb10-4da15d803a82" xlink:to="loc_us-gaap_ClassOfStockDomain_020c529d-c0fd-445f-95d0-753643924d71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_SeriesBPerpetualNonConvertiblePreferredStockMember_ab58284f-9136-43e0-9b5f-8424fa626eb9" xlink:href="sncr-20230930.xsd#sncr_SeriesBPerpetualNonConvertiblePreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_020c529d-c0fd-445f-95d0-753643924d71" xlink:to="loc_sncr_SeriesBPerpetualNonConvertiblePreferredStockMember_ab58284f-9136-43e0-9b5f-8424fa626eb9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_c71ebca8-1cc7-4e09-88bc-9b6151cdabe9" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_19ff802e-d688-4017-95b5-719d26ad4cde" xlink:to="loc_srt_RangeAxis_c71ebca8-1cc7-4e09-88bc-9b6151cdabe9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_c71ebca8-1cc7-4e09-88bc-9b6151cdabe9_default" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_c71ebca8-1cc7-4e09-88bc-9b6151cdabe9" xlink:to="loc_srt_RangeMember_c71ebca8-1cc7-4e09-88bc-9b6151cdabe9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_3c6991dc-bbb0-4df3-8029-6599a4a6c28a" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_c71ebca8-1cc7-4e09-88bc-9b6151cdabe9" xlink:to="loc_srt_RangeMember_3c6991dc-bbb0-4df3-8029-6599a4a6c28a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_b107500b-977a-41f3-a7c2-213a0079a9d0" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_3c6991dc-bbb0-4df3-8029-6599a4a6c28a" xlink:to="loc_srt_MinimumMember_b107500b-977a-41f3-a7c2-213a0079a9d0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_3008b521-00dc-4f74-ade7-a374c0049e6e" xlink:href="https://xbrl.fasb.org/srt/2023/elts/srt-2023.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_3c6991dc-bbb0-4df3-8029-6599a4a6c28a" xlink:to="loc_srt_MaximumMember_3008b521-00dc-4f74-ade7-a374c0049e6e" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-roles-2023.xsd#eedm"/>
  <link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesNoncurrentAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2023/elts/us-gaap-2023.xsd#us-gaap_LiabilitiesNoncurrentAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_LeaseLiabilityNoncurrent_aa70489a-5cb9-4bfc-9b19-6ee586128e20" xlink:href="sncr-20230930.xsd#sncr_LeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesNoncurrentAbstract" xlink:to="loc_sncr_LeaseLiabilityNoncurrent_aa70489a-5cb9-4bfc-9b19-6ee586128e20" xlink:type="arc" order="1"/>
  </link:definitionLink>
</link:linkbase>
