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

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2021 Workiva-->
<!--r:70275cb1-ef91-451d-8be7-2d8bead52df2,g:bfc69a2a-2210-4a72-9e12-1438f6caf7e1-->
<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/CoverPage" xlink:type="simple" xlink:href="sncr-20210630.xsd#CoverPage"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CoverPage" xlink:type="extended" id="i1c45349abddd4d49b768d54309b1acd4_CoverPage">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_efec6e6e-880e-42aa-bc55-0fac20edb2e2" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_DocumentType_efec6e6e-880e-42aa-bc55-0fac20edb2e2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_f7b5bd2e-1691-4dd5-adb3-33020cc052d4" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_DocumentQuarterlyReport_f7b5bd2e-1691-4dd5-adb3-33020cc052d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_86249b4c-b163-4173-b0d0-50fdb0f80075" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_DocumentPeriodEndDate_86249b4c-b163-4173-b0d0-50fdb0f80075" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_ac25a60e-7939-4db9-ac83-02eee815e041" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_DocumentTransitionReport_ac25a60e-7939-4db9-ac83-02eee815e041" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_984d06a5-c39a-4d4f-8b99-8d91ad508836" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_EntityFileNumber_984d06a5-c39a-4d4f-8b99-8d91ad508836" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_06d994b3-1473-433e-98e5-4da3a1a080b9" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_EntityRegistrantName_06d994b3-1473-433e-98e5-4da3a1a080b9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_c42b3d9a-2cdf-415a-b2e4-8cbb5742ab7b" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_EntityIncorporationStateCountryCode_c42b3d9a-2cdf-415a-b2e4-8cbb5742ab7b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_f3112650-96d6-4670-a247-72d31d2ddcfe" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_EntityTaxIdentificationNumber_f3112650-96d6-4670-a247-72d31d2ddcfe" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_457ccf9d-2f91-4591-844f-130cc19a6bec" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_EntityAddressAddressLine1_457ccf9d-2f91-4591-844f-130cc19a6bec" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_1524a9ea-8277-449f-9f92-68651ee6b531" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_EntityAddressAddressLine2_1524a9ea-8277-449f-9f92-68651ee6b531" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_3d0f44e9-13fb-48bf-8b6b-c82690fb2e34" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_EntityAddressCityOrTown_3d0f44e9-13fb-48bf-8b6b-c82690fb2e34" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_ccfc64fe-57e2-4a43-99cb-8aae202b11dc" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_EntityAddressStateOrProvince_ccfc64fe-57e2-4a43-99cb-8aae202b11dc" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_4a55684c-6ecf-481d-838c-0842bfef38ca" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_EntityAddressPostalZipCode_4a55684c-6ecf-481d-838c-0842bfef38ca" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_8ccb1a53-8d9a-4d87-9744-ee206fccfbb8" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_CityAreaCode_8ccb1a53-8d9a-4d87-9744-ee206fccfbb8" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_707a6466-54ad-4ce1-8171-3b941eba568e" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_LocalPhoneNumber_707a6466-54ad-4ce1-8171-3b941eba568e" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_f648c25e-f0c2-4551-befe-b4446ef6bfb1" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_EntityCurrentReportingStatus_f648c25e-f0c2-4551-befe-b4446ef6bfb1" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_26aeaace-ef73-4855-a9c1-b7ff3c7496be" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_EntityInteractiveDataCurrent_26aeaace-ef73-4855-a9c1-b7ff3c7496be" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_b983bda3-5199-49bc-bc26-f86bef799575" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_EntityFilerCategory_b983bda3-5199-49bc-bc26-f86bef799575" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_d4c27378-1bea-4281-a9cb-65ac8fd37b2a" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_EntitySmallBusiness_d4c27378-1bea-4281-a9cb-65ac8fd37b2a" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_acb292fb-6e89-4f7b-a884-3003ec1a9bdc" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_EntityEmergingGrowthCompany_acb292fb-6e89-4f7b-a884-3003ec1a9bdc" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_b6403dc2-a71f-4cff-9051-9193686919cd" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_EntityShellCompany_b6403dc2-a71f-4cff-9051-9193686919cd" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_805277bc-d912-4caf-9eda-c84c3e045846" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_Security12bTitle_805277bc-d912-4caf-9eda-c84c3e045846" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_ed0c0cf6-4d0b-41f8-a565-7d4c0ba8b861" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_TradingSymbol_ed0c0cf6-4d0b-41f8-a565-7d4c0ba8b861" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_9e00e4bf-9f0a-497d-b3f8-224d3d952cf9" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_SecurityExchangeName_9e00e4bf-9f0a-497d-b3f8-224d3d952cf9" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_d7a7e63a-7d84-422e-9582-a602ba90a865" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_d7a7e63a-7d84-422e-9582-a602ba90a865" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_cc6f80e8-16dd-41f6-bba0-6a032640c417" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_EntityCentralIndexKey_cc6f80e8-16dd-41f6-bba0-6a032640c417" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_1df9af81-bcaf-412b-8e23-7232416be553" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_AmendmentFlag_1df9af81-bcaf-412b-8e23-7232416be553" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_e8db9bb5-4cc0-40c8-bdd3-c9d8a9b53934" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_CurrentFiscalYearEndDate_e8db9bb5-4cc0-40c8-bdd3-c9d8a9b53934" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_8d6a02b4-3e39-4753-a9e3-44f4ed4c3a6a" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_DocumentFiscalYearFocus_8d6a02b4-3e39-4753-a9e3-44f4ed4c3a6a" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_6f86042c-c0f3-4fae-9370-cf2f34e7c986" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_DocumentFiscalPeriodFocus_6f86042c-c0f3-4fae-9370-cf2f34e7c986" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_ddfc89b3-2a92-412b-b856-1b0eaa830287" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_af8e11dd-d954-4924-9f44-f29e6e2d90f4" xlink:to="loc_dei_DocumentInformationTable_ddfc89b3-2a92-412b-b856-1b0eaa830287" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_84f4e3a2-4716-4a23-8dfa-25ca67dcf67e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_ddfc89b3-2a92-412b-b856-1b0eaa830287" xlink:to="loc_us-gaap_StatementClassOfStockAxis_84f4e3a2-4716-4a23-8dfa-25ca67dcf67e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_84f4e3a2-4716-4a23-8dfa-25ca67dcf67e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_84f4e3a2-4716-4a23-8dfa-25ca67dcf67e" xlink:to="loc_us-gaap_ClassOfStockDomain_84f4e3a2-4716-4a23-8dfa-25ca67dcf67e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_41d5da0b-575d-4ec5-8984-67622a499483" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_84f4e3a2-4716-4a23-8dfa-25ca67dcf67e" xlink:to="loc_us-gaap_ClassOfStockDomain_41d5da0b-575d-4ec5-8984-67622a499483" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_c94932f5-840f-44a3-ad20-2110aec50d2b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_41d5da0b-575d-4ec5-8984-67622a499483" xlink:to="loc_us-gaap_CommonStockMember_c94932f5-840f-44a3-ad20-2110aec50d2b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_EightPointThreeSevenFivePercent2500ParValueSeniorNotesDue2026Member_71770d45-6023-4a9b-a40c-d2dd4d2feb25" xlink:href="sncr-20210630.xsd#sncr_EightPointThreeSevenFivePercent2500ParValueSeniorNotesDue2026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_41d5da0b-575d-4ec5-8984-67622a499483" xlink:to="loc_sncr_EightPointThreeSevenFivePercent2500ParValueSeniorNotesDue2026Member_71770d45-6023-4a9b-a40c-d2dd4d2feb25" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSUnaudited" xlink:type="simple" xlink:href="sncr-20210630.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETSUnaudited"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSUnaudited" xlink:type="extended" id="ie03117b707404ff5974d58b06a9c2e9b_CONDENSEDCONSOLIDATEDBALANCESHEETSUnaudited">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_fd1cc388-eee9-4476-b3fe-92c226ab47dc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_c6133628-9628-43cf-afc9-ea340fa22d99" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fd1cc388-eee9-4476-b3fe-92c226ab47dc" xlink:to="loc_us-gaap_AssetsAbstract_c6133628-9628-43cf-afc9-ea340fa22d99" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_afd5f6ff-ce7e-426d-b9ce-86e534078197" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_c6133628-9628-43cf-afc9-ea340fa22d99" xlink:to="loc_us-gaap_AssetsCurrentAbstract_afd5f6ff-ce7e-426d-b9ce-86e534078197" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_252e2b1f-a888-4922-9458-0550f48d6cce" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_afd5f6ff-ce7e-426d-b9ce-86e534078197" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_252e2b1f-a888-4922-9458-0550f48d6cce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_b8c7996c-c983-4966-80e9-bc24bb04ae01" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_afd5f6ff-ce7e-426d-b9ce-86e534078197" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_b8c7996c-c983-4966-80e9-bc24bb04ae01" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_9342f7e1-eb89-4abc-ba89-5e63630b3a96" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_afd5f6ff-ce7e-426d-b9ce-86e534078197" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_9342f7e1-eb89-4abc-ba89-5e63630b3a96" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_7f461128-8c58-41cf-9c05-413833c30114" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_afd5f6ff-ce7e-426d-b9ce-86e534078197" xlink:to="loc_us-gaap_AssetsCurrent_7f461128-8c58-41cf-9c05-413833c30114" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNoncurrentAbstract_27b6a0b7-aa5d-49fe-99d5-5f937d469127" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_c6133628-9628-43cf-afc9-ea340fa22d99" xlink:to="loc_us-gaap_AssetsNoncurrentAbstract_27b6a0b7-aa5d-49fe-99d5-5f937d469127" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_848c15df-aff4-4105-92b3-3d3ffb26efea" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_27b6a0b7-aa5d-49fe-99d5-5f937d469127" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_848c15df-aff4-4105-92b3-3d3ffb26efea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_865416b8-da59-4475-9657-4653c79f9d56" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_27b6a0b7-aa5d-49fe-99d5-5f937d469127" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_865416b8-da59-4475-9657-4653c79f9d56" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_3098844c-cc3b-46a9-875e-ab9417b2fdf7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_27b6a0b7-aa5d-49fe-99d5-5f937d469127" xlink:to="loc_us-gaap_Goodwill_3098844c-cc3b-46a9-875e-ab9417b2fdf7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_831c3d8f-9f62-44dc-a347-4c68b0e52da0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_27b6a0b7-aa5d-49fe-99d5-5f937d469127" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_831c3d8f-9f62-44dc-a347-4c68b0e52da0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesAndLoansReceivableNetNoncurrent_19dccfb6-0cfa-4429-9d25-8c3f09af4c7e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NotesAndLoansReceivableNetNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_27b6a0b7-aa5d-49fe-99d5-5f937d469127" xlink:to="loc_us-gaap_NotesAndLoansReceivableNetNoncurrent_19dccfb6-0cfa-4429-9d25-8c3f09af4c7e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_25396f26-ce75-4578-854f-c13d60cfabd5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_27b6a0b7-aa5d-49fe-99d5-5f937d469127" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_25396f26-ce75-4578-854f-c13d60cfabd5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsNoncurrent_a425c4da-7f9c-475d-acf8-9face65663b5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsNoncurrentAbstract_27b6a0b7-aa5d-49fe-99d5-5f937d469127" xlink:to="loc_us-gaap_AssetsNoncurrent_a425c4da-7f9c-475d-acf8-9face65663b5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_c84d3e79-c45d-4e13-9a08-b94282f54264" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_c6133628-9628-43cf-afc9-ea340fa22d99" xlink:to="loc_us-gaap_Assets_c84d3e79-c45d-4e13-9a08-b94282f54264" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_f5f94900-aac0-4291-83cf-58df7c424884" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fd1cc388-eee9-4476-b3fe-92c226ab47dc" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_f5f94900-aac0-4291-83cf-58df7c424884" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_cce8c14b-2ee4-4d2e-8769-e8bf3bd1b79a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_f5f94900-aac0-4291-83cf-58df7c424884" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_cce8c14b-2ee4-4d2e-8769-e8bf3bd1b79a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_3e8ef0e1-6766-43fa-ad41-47e539d19435" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_cce8c14b-2ee4-4d2e-8769-e8bf3bd1b79a" xlink:to="loc_us-gaap_AccountsPayableCurrent_3e8ef0e1-6766-43fa-ad41-47e539d19435" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_9f619ac4-3566-42dc-b185-6950c93eeb4d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_cce8c14b-2ee4-4d2e-8769-e8bf3bd1b79a" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_9f619ac4-3566-42dc-b185-6950c93eeb4d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_9fac1289-2338-4990-b724-bcf9a9b2a9c4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_cce8c14b-2ee4-4d2e-8769-e8bf3bd1b79a" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_9fac1289-2338-4990-b724-bcf9a9b2a9c4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtCurrent_95bf3e3c-9433-424c-b451-4cf986310686" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_cce8c14b-2ee4-4d2e-8769-e8bf3bd1b79a" xlink:to="loc_us-gaap_DebtCurrent_95bf3e3c-9433-424c-b451-4cf986310686" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_1191f3eb-04bb-4ff1-86b9-f2a84699614b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_cce8c14b-2ee4-4d2e-8769-e8bf3bd1b79a" xlink:to="loc_us-gaap_LiabilitiesCurrent_1191f3eb-04bb-4ff1-86b9-f2a84699614b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_77d7c062-93ec-4ed1-9566-427fb874b655" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_f5f94900-aac0-4291-83cf-58df7c424884" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_77d7c062-93ec-4ed1-9566-427fb874b655" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_efbac0a5-dc8f-4241-9134-6de028a88559" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_f5f94900-aac0-4291-83cf-58df7c424884" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_efbac0a5-dc8f-4241-9134-6de028a88559" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_7484603b-e8c4-4758-badd-feeb098e5685" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_f5f94900-aac0-4291-83cf-58df7c424884" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_7484603b-e8c4-4758-badd-feeb098e5685" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_LeaseLiabilityNoncurrent_cc036fdd-c01a-445c-a8d8-9be256625039" xlink:href="sncr-20210630.xsd#sncr_LeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_f5f94900-aac0-4291-83cf-58df7c424884" xlink:to="loc_sncr_LeaseLiabilityNoncurrent_cc036fdd-c01a-445c-a8d8-9be256625039" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_98825fed-3e4d-46e9-9c69-4eac9152156a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_f5f94900-aac0-4291-83cf-58df7c424884" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_98825fed-3e4d-46e9-9c69-4eac9152156a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_RedeemableNoncontrollingInterest_b2434a66-ac2f-46e2-a636-7cc2332234d8" xlink:href="sncr-20210630.xsd#sncr_RedeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_f5f94900-aac0-4291-83cf-58df7c424884" xlink:to="loc_sncr_RedeemableNoncontrollingInterest_b2434a66-ac2f-46e2-a636-7cc2332234d8" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_18ad2284-0916-4057-95e9-cec9ea024c14" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_f5f94900-aac0-4291-83cf-58df7c424884" xlink:to="loc_us-gaap_Liabilities_18ad2284-0916-4057-95e9-cec9ea024c14" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_cb58b83e-567e-4089-b8fb-950cabdb83c8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_f5f94900-aac0-4291-83cf-58df7c424884" xlink:to="loc_us-gaap_CommitmentsAndContingencies_cb58b83e-567e-4089-b8fb-950cabdb83c8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_433f08a8-1ce9-44e4-865f-0adcfd75b244" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityCarryingAmountAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_f5f94900-aac0-4291-83cf-58df7c424884" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountAttributableToParent_433f08a8-1ce9-44e4-865f-0adcfd75b244" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_55448eb4-6d2d-4798-9fb9-45f99d5320bf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_f5f94900-aac0-4291-83cf-58df7c424884" xlink:to="loc_us-gaap_StockholdersEquityAbstract_55448eb4-6d2d-4798-9fb9-45f99d5320bf" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_5630aaa5-7a26-4606-a057-a57b9abad541" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_55448eb4-6d2d-4798-9fb9-45f99d5320bf" xlink:to="loc_us-gaap_CommonStockValue_5630aaa5-7a26-4606-a057-a57b9abad541" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValue_4f0e4ece-dc0f-4209-a20d-6074a4af448e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_55448eb4-6d2d-4798-9fb9-45f99d5320bf" xlink:to="loc_us-gaap_TreasuryStockValue_4f0e4ece-dc0f-4209-a20d-6074a4af448e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_9cd514b9-d657-4037-b863-e0100b0aa22d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_55448eb4-6d2d-4798-9fb9-45f99d5320bf" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_9cd514b9-d657-4037-b863-e0100b0aa22d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_3c1aa358-536b-4acf-a947-b36be50acc6c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_55448eb4-6d2d-4798-9fb9-45f99d5320bf" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_3c1aa358-536b-4acf-a947-b36be50acc6c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_d6fa91ae-9df6-4f3c-baf1-c4d73dbb113e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_55448eb4-6d2d-4798-9fb9-45f99d5320bf" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_d6fa91ae-9df6-4f3c-baf1-c4d73dbb113e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_0fa468f7-de16-4eaa-9644-30b81b4f6e2e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_55448eb4-6d2d-4798-9fb9-45f99d5320bf" xlink:to="loc_us-gaap_StockholdersEquity_0fa468f7-de16-4eaa-9644-30b81b4f6e2e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_486ec69d-e044-452a-83e3-8f353343829f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_f5f94900-aac0-4291-83cf-58df7c424884" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_486ec69d-e044-452a-83e3-8f353343829f" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_04129a53-1b68-44a3-9f8c-703c2cf13bd7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_fd1cc388-eee9-4476-b3fe-92c226ab47dc" xlink:to="loc_us-gaap_StatementTable_04129a53-1b68-44a3-9f8c-703c2cf13bd7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_23d5321b-ba89-46db-91f2-e43e2f2b5e5b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_04129a53-1b68-44a3-9f8c-703c2cf13bd7" xlink:to="loc_us-gaap_StatementClassOfStockAxis_23d5321b-ba89-46db-91f2-e43e2f2b5e5b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_23d5321b-ba89-46db-91f2-e43e2f2b5e5b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_23d5321b-ba89-46db-91f2-e43e2f2b5e5b" xlink:to="loc_us-gaap_ClassOfStockDomain_23d5321b-ba89-46db-91f2-e43e2f2b5e5b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_52c4b805-2672-441d-8b86-cb138bb74214" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_23d5321b-ba89-46db-91f2-e43e2f2b5e5b" xlink:to="loc_us-gaap_ClassOfStockDomain_52c4b805-2672-441d-8b86-cb138bb74214" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_61be4226-8749-4596-86d2-4a0a0429c984" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_52c4b805-2672-441d-8b86-cb138bb74214" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_61be4226-8749-4596-86d2-4a0a0429c984" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesBPreferredStockMember_5515a7b7-2ec2-4718-b658-8090d51372cc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SeriesBPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_52c4b805-2672-441d-8b86-cb138bb74214" xlink:to="loc_us-gaap_SeriesBPreferredStockMember_5515a7b7-2ec2-4718-b658-8090d51372cc" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSUnauditedParenthetical" xlink:type="simple" xlink:href="sncr-20210630.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETSUnauditedParenthetical"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSUnauditedParenthetical" xlink:type="extended" id="i081639f70317480f96fb9be60e42bd76_CONDENSEDCONSOLIDATEDBALANCESHEETSUnauditedParenthetical">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_19113455-5c7a-43c0-a955-8a480dc04050" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityParOrStatedValuePerShare_47316768-a1d5-41e0-9514-7e871db801fd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_19113455-5c7a-43c0-a955-8a480dc04050" xlink:to="loc_us-gaap_TemporaryEquityParOrStatedValuePerShare_47316768-a1d5-41e0-9514-7e871db801fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesAuthorized_70c71107-adad-4992-b1e0-55fffc3a3516" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquitySharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_19113455-5c7a-43c0-a955-8a480dc04050" xlink:to="loc_us-gaap_TemporaryEquitySharesAuthorized_70c71107-adad-4992-b1e0-55fffc3a3516" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesIssued_c61b2fa9-99fd-4498-8bef-25536cb58b27" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquitySharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_19113455-5c7a-43c0-a955-8a480dc04050" xlink:to="loc_us-gaap_TemporaryEquitySharesIssued_c61b2fa9-99fd-4498-8bef-25536cb58b27" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_27b9ce34-0bba-4ce1-96eb-cba72ffaa557" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_19113455-5c7a-43c0-a955-8a480dc04050" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_27b9ce34-0bba-4ce1-96eb-cba72ffaa557" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_18983d0e-eed8-42c2-8c53-514a02ef1cb9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_19113455-5c7a-43c0-a955-8a480dc04050" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_18983d0e-eed8-42c2-8c53-514a02ef1cb9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_02996366-bef2-4205-87be-6487cec897e9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_19113455-5c7a-43c0-a955-8a480dc04050" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_02996366-bef2-4205-87be-6487cec897e9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_4e0870ef-52f0-4064-b946-9dcda5b15868" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_19113455-5c7a-43c0-a955-8a480dc04050" xlink:to="loc_us-gaap_CommonStockSharesIssued_4e0870ef-52f0-4064-b946-9dcda5b15868" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_626c3f3c-f33b-44f1-9331-2f7c73c20d72" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_19113455-5c7a-43c0-a955-8a480dc04050" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_626c3f3c-f33b-44f1-9331-2f7c73c20d72" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockShares_eeff2acc-e5dc-4829-a0d9-7ab8a4e55ec1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_19113455-5c7a-43c0-a955-8a480dc04050" xlink:to="loc_us-gaap_TreasuryStockShares_eeff2acc-e5dc-4829-a0d9-7ab8a4e55ec1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_f8665e57-89bb-4dda-a0de-b947e07061c9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_19113455-5c7a-43c0-a955-8a480dc04050" xlink:to="loc_us-gaap_StatementTable_f8665e57-89bb-4dda-a0de-b947e07061c9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_813b3b19-c0c9-4c15-bbdb-7c346a51f12b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_f8665e57-89bb-4dda-a0de-b947e07061c9" xlink:to="loc_us-gaap_StatementClassOfStockAxis_813b3b19-c0c9-4c15-bbdb-7c346a51f12b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_813b3b19-c0c9-4c15-bbdb-7c346a51f12b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_813b3b19-c0c9-4c15-bbdb-7c346a51f12b" xlink:to="loc_us-gaap_ClassOfStockDomain_813b3b19-c0c9-4c15-bbdb-7c346a51f12b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_73851223-05a0-488e-b848-53c0d02d05f7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_813b3b19-c0c9-4c15-bbdb-7c346a51f12b" xlink:to="loc_us-gaap_ClassOfStockDomain_73851223-05a0-488e-b848-53c0d02d05f7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_68a67382-2d20-4aff-8606-2225d0914732" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_73851223-05a0-488e-b848-53c0d02d05f7" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_68a67382-2d20-4aff-8606-2225d0914732" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesBPreferredStockMember_97bf6380-19f1-419c-8aee-cf0ab6f868b9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SeriesBPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_73851223-05a0-488e-b848-53c0d02d05f7" xlink:to="loc_us-gaap_SeriesBPreferredStockMember_97bf6380-19f1-419c-8aee-cf0ab6f868b9" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITYUnaudited" xlink:type="simple" xlink:href="sncr-20210630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITYUnaudited"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITYUnaudited" xlink:type="extended" id="i0a513e38e003468db8a65e0819076ff2_CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITYUnaudited">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_39c12bc4-93f0-435c-abc1-c25dadbcdd6d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_39c12bc4-93f0-435c-abc1-c25dadbcdd6d" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_c4dec446-d4a2-46a8-aded-c4af6e2a24b4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:to="loc_us-gaap_CommonStockSharesIssued_c4dec446-d4a2-46a8-aded-c4af6e2a24b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_089cfdb7-2c57-4e6c-8c3b-ca8b9980943f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_089cfdb7-2c57-4e6c-8c3b-ca8b9980943f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_62030f6d-cc62-4067-b6c8-18cd71d293e9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_62030f6d-cc62-4067-b6c8-18cd71d293e9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_ee027ab1-87cc-4e06-a16e-d2f98263ce26" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_ee027ab1-87cc-4e06-a16e-d2f98263ce26" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_a667936b-e522-4f7e-8b3b-9d9267641744" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_a667936b-e522-4f7e-8b3b-9d9267641744" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPreferredStock_248f0b1f-0bda-49bf-ba18-984143e6cb33" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DividendsPreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:to="loc_us-gaap_DividendsPreferredStock_248f0b1f-0bda-49bf-ba18-984143e6cb33" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts_2aee8774-e4b3-4cea-8d94-278e101bd8f3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts_2aee8774-e4b3-4cea-8d94-278e101bd8f3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_b3f8f462-b25e-4b7e-b3f2-6166c049d581" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_b3f8f462-b25e-4b7e-b3f2-6166c049d581" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_28f91783-9f33-4b21-97c9-50108a942345" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_28f91783-9f33-4b21-97c9-50108a942345" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_AdjustmentsToAdditionalPaidInCapitalStockIssuedCommonStockIssuanceCosts_c119a74f-e7d6-47c8-9d3c-ccfc48eaecc7" xlink:href="sncr-20210630.xsd#sncr_AdjustmentsToAdditionalPaidInCapitalStockIssuedCommonStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:to="loc_sncr_AdjustmentsToAdditionalPaidInCapitalStockIssuedCommonStockIssuanceCosts_c119a74f-e7d6-47c8-9d3c-ccfc48eaecc7" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesRetired_12c57bc1-749b-42f6-ad04-e2528615bd1f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockSharesRetired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:to="loc_us-gaap_TreasuryStockSharesRetired_12c57bc1-749b-42f6-ad04-e2528615bd1f" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockRetiredCostMethodAmount_c1d39aa1-df3a-41c0-af67-1d6924e8a56c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockRetiredCostMethodAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:to="loc_us-gaap_TreasuryStockRetiredCostMethodAmount_c1d39aa1-df3a-41c0-af67-1d6924e8a56c" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_4a366ebb-7951-4dd5-a3cf-6a5fbb458c38" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_4a366ebb-7951-4dd5-a3cf-6a5fbb458c38" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_49352439-abaf-46a6-8888-1b411254ad53" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:to="loc_us-gaap_ProfitLoss_49352439-abaf-46a6-8888-1b411254ad53" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestChangeInRedemptionValue_4bbc134a-265d-4a1f-8037-a01afe07121f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MinorityInterestChangeInRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:to="loc_us-gaap_MinorityInterestChangeInRedemptionValue_4bbc134a-265d-4a1f-8037-a01afe07121f" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_a4ff8bff-5cfa-4040-a068-dd9f105ba92d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_2663f3a9-fd5f-4bf5-9c27-5081401bbf44" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTax_a4ff8bff-5cfa-4040-a068-dd9f105ba92d" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_cab6ddaf-d13c-4775-9d47-921eb4faf625" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_f02347bc-97e5-4af4-b096-7a435dbff6de" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountingStandardsUpdateExtensibleList_f38c6042-1e4e-41db-98d1-9bef66132d9f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccountingStandardsUpdateExtensibleList"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_39c12bc4-93f0-435c-abc1-c25dadbcdd6d" xlink:to="loc_us-gaap_AccountingStandardsUpdateExtensibleList_f38c6042-1e4e-41db-98d1-9bef66132d9f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_eb0aa9b4-ea75-46f9-9325-d99592d67259" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_39c12bc4-93f0-435c-abc1-c25dadbcdd6d" xlink:to="loc_us-gaap_StatementTable_eb0aa9b4-ea75-46f9-9325-d99592d67259" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_1661dcd3-5a84-447c-99bc-d8e9d247ec8e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_eb0aa9b4-ea75-46f9-9325-d99592d67259" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_1661dcd3-5a84-447c-99bc-d8e9d247ec8e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_1661dcd3-5a84-447c-99bc-d8e9d247ec8e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_1661dcd3-5a84-447c-99bc-d8e9d247ec8e" xlink:to="loc_us-gaap_EquityComponentDomain_1661dcd3-5a84-447c-99bc-d8e9d247ec8e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_7b110aec-61af-4e92-8c5e-a6eed8b25f78" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_1661dcd3-5a84-447c-99bc-d8e9d247ec8e" xlink:to="loc_us-gaap_EquityComponentDomain_7b110aec-61af-4e92-8c5e-a6eed8b25f78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_f7080dc6-57fc-42e7-a185-f6a8f30e0433" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_7b110aec-61af-4e92-8c5e-a6eed8b25f78" xlink:to="loc_us-gaap_CommonStockMember_f7080dc6-57fc-42e7-a185-f6a8f30e0433" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockMember_0cf7831c-6875-490e-995b-7b6568e890e1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_7b110aec-61af-4e92-8c5e-a6eed8b25f78" xlink:to="loc_us-gaap_TreasuryStockMember_0cf7831c-6875-490e-995b-7b6568e890e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_642fc7c6-52c9-4a67-bf23-2f32186552da" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_7b110aec-61af-4e92-8c5e-a6eed8b25f78" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_642fc7c6-52c9-4a67-bf23-2f32186552da" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AociIncludingPortionAttributableToNoncontrollingInterestMember_94841156-f9d9-4b7d-a142-e13730a0449e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AociIncludingPortionAttributableToNoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_7b110aec-61af-4e92-8c5e-a6eed8b25f78" xlink:to="loc_us-gaap_AociIncludingPortionAttributableToNoncontrollingInterestMember_94841156-f9d9-4b7d-a142-e13730a0449e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_2d94bde4-084f-487d-8af6-90c552bd9324" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_7b110aec-61af-4e92-8c5e-a6eed8b25f78" xlink:to="loc_us-gaap_RetainedEarningsMember_2d94bde4-084f-487d-8af6-90c552bd9324" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_3b8dfe63-d45a-49e7-ba8b-34a241182651" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_eb0aa9b4-ea75-46f9-9325-d99592d67259" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_3b8dfe63-d45a-49e7-ba8b-34a241182651" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_3b8dfe63-d45a-49e7-ba8b-34a241182651_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_3b8dfe63-d45a-49e7-ba8b-34a241182651" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_3b8dfe63-d45a-49e7-ba8b-34a241182651_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_a607238a-6f3c-4227-b41a-428c4b10274b" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_3b8dfe63-d45a-49e7-ba8b-34a241182651" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_a607238a-6f3c-4227-b41a-428c4b10274b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_82928082-d44f-4fda-a020-6e69ab7ba43b" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_a607238a-6f3c-4227-b41a-428c4b10274b" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_82928082-d44f-4fda-a020-6e69ab7ba43b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUnaudited" xlink:type="simple" xlink:href="sncr-20210630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUnaudited"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUnaudited" xlink:type="extended" id="i4a2a49b927874ca7a395af2b5ee3f50b_CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUnaudited">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_58b5ac6f-dd22-4de4-872b-dd30454d8ae7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_d50cc41d-54b8-4fea-9918-2c3de5a8c2e8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_58b5ac6f-dd22-4de4-872b-dd30454d8ae7" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_d50cc41d-54b8-4fea-9918-2c3de5a8c2e8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_ea360fb4-a3a4-4970-bfe7-f7ddc0baafcb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_d50cc41d-54b8-4fea-9918-2c3de5a8c2e8" xlink:to="loc_us-gaap_ProfitLoss_ea360fb4-a3a4-4970-bfe7-f7ddc0baafcb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_183a7ef5-301a-4fa8-b468-cf2f40d37b3f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_d50cc41d-54b8-4fea-9918-2c3de5a8c2e8" xlink:to="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_183a7ef5-301a-4fa8-b468-cf2f40d37b3f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DepreciationDepletionandAmortizationNetofImpairment_c1e5987f-69a8-4460-a1f9-5c7ec0b96f65" xlink:href="sncr-20210630.xsd#sncr_DepreciationDepletionandAmortizationNetofImpairment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_183a7ef5-301a-4fa8-b468-cf2f40d37b3f" xlink:to="loc_sncr_DepreciationDepletionandAmortizationNetofImpairment_c1e5987f-69a8-4460-a1f9-5c7ec0b96f65" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnDispositionOfAssets_8fe923a6-6a56-40a7-9975-53ba3804a888" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GainLossOnDispositionOfAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_183a7ef5-301a-4fa8-b468-cf2f40d37b3f" xlink:to="loc_us-gaap_GainLossOnDispositionOfAssets_8fe923a6-6a56-40a7-9975-53ba3804a888" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainLossOnDispositionOfIntangibleAssets_e38b848a-f7b5-475c-838e-7e8a8682c527" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GainLossOnDispositionOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_183a7ef5-301a-4fa8-b468-cf2f40d37b3f" xlink:to="loc_us-gaap_GainLossOnDispositionOfIntangibleAssets_e38b848a-f7b5-475c-838e-7e8a8682c527" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_d5b1f916-981b-4f8c-8db5-ed06ee22c0a6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_183a7ef5-301a-4fa8-b468-cf2f40d37b3f" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_d5b1f916-981b-4f8c-8db5-ed06ee22c0a6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_1f8943b0-1784-4fc5-a715-8375c7c1f0ad" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_183a7ef5-301a-4fa8-b468-cf2f40d37b3f" xlink:to="loc_us-gaap_ShareBasedCompensation_1f8943b0-1784-4fc5-a715-8375c7c1f0ad" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseImpairmentLoss_ecab8d1d-426f-49b6-ad0c-11b365ce4d3a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLeaseImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_183a7ef5-301a-4fa8-b468-cf2f40d37b3f" xlink:to="loc_us-gaap_OperatingLeaseImpairmentLoss_ecab8d1d-426f-49b6-ad0c-11b365ce4d3a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_df50299f-23a0-407c-a03a-ff02c2b4696c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_183a7ef5-301a-4fa8-b468-cf2f40d37b3f" xlink:to="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_df50299f-23a0-407c-a03a-ff02c2b4696c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_48b69ba2-7342-4e41-b75f-247438e55ff4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_df50299f-23a0-407c-a03a-ff02c2b4696c" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_48b69ba2-7342-4e41-b75f-247438e55ff4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_78a06fe0-1593-4c6b-946e-d340379eb488" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_df50299f-23a0-407c-a03a-ff02c2b4696c" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_78a06fe0-1593-4c6b-946e-d340379eb488" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_2b1d9e47-267d-4785-beba-7f1a13cc9be1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_df50299f-23a0-407c-a03a-ff02c2b4696c" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_2b1d9e47-267d-4785-beba-7f1a13cc9be1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_ab570adc-8ea4-40fa-a611-d46b350dbfba" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_df50299f-23a0-407c-a03a-ff02c2b4696c" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedLiabilities_ab570adc-8ea4-40fa-a611-d46b350dbfba" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_f7e40e24-027e-4ae3-ada9-324ce44b4952" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_df50299f-23a0-407c-a03a-ff02c2b4696c" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingAssets_f7e40e24-027e-4ae3-ada9-324ce44b4952" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_3cb3cc8b-8940-4b32-bfe9-c95a424dbd71" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_df50299f-23a0-407c-a03a-ff02c2b4696c" xlink:to="loc_us-gaap_IncreaseDecreaseInContractWithCustomerLiability_3cb3cc8b-8940-4b32-bfe9-c95a424dbd71" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_fea820aa-3406-4d5a-a0c3-7c006ea0e6f2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInOtherOperatingLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_df50299f-23a0-407c-a03a-ff02c2b4696c" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherOperatingLiabilities_fea820aa-3406-4d5a-a0c3-7c006ea0e6f2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_da518170-6e0b-423c-8cab-13061ebbba1b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_d50cc41d-54b8-4fea-9918-2c3de5a8c2e8" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_da518170-6e0b-423c-8cab-13061ebbba1b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_d2b497a9-6d5a-4126-a06c-2479eabcbd9d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_58b5ac6f-dd22-4de4-872b-dd30454d8ae7" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_d2b497a9-6d5a-4126-a06c-2479eabcbd9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_5074d05c-b9fe-4ef2-b957-da3b00c9c10d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_d2b497a9-6d5a-4126-a06c-2479eabcbd9d" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_5074d05c-b9fe-4ef2-b957-da3b00c9c10d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForSoftware_9b2fc73c-967e-42ae-bcdf-33a354cd4667" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsForSoftware"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_d2b497a9-6d5a-4126-a06c-2479eabcbd9d" xlink:to="loc_us-gaap_PaymentsForSoftware_9b2fc73c-967e-42ae-bcdf-33a354cd4667" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfIntangibleAssets_9a7d073f-ac17-4928-9d03-79997f2c9322" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromSaleOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_d2b497a9-6d5a-4126-a06c-2479eabcbd9d" xlink:to="loc_us-gaap_ProceedsFromSaleOfIntangibleAssets_9a7d073f-ac17-4928-9d03-79997f2c9322" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleAndMaturityOfAvailableForSaleSecurities_8fc9c6d0-d722-48cc-8a8e-f9680b3cc73e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromSaleAndMaturityOfAvailableForSaleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_d2b497a9-6d5a-4126-a06c-2479eabcbd9d" xlink:to="loc_us-gaap_ProceedsFromSaleAndMaturityOfAvailableForSaleSecurities_8fc9c6d0-d722-48cc-8a8e-f9680b3cc73e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_ffae7617-b1b1-49fe-a56d-df5e274d02f1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_d2b497a9-6d5a-4126-a06c-2479eabcbd9d" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_ffae7617-b1b1-49fe-a56d-df5e274d02f1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_79528e7e-0234-47aa-bbce-5a04c9990576" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_58b5ac6f-dd22-4de4-872b-dd30454d8ae7" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_79528e7e-0234-47aa-bbce-5a04c9990576" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions_b5dbe863-7775-465c-be1c-77030042bde1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_79528e7e-0234-47aa-bbce-5a04c9990576" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfSharesUnderIncentiveAndShareBasedCompensationPlansIncludingStockOptions_b5dbe863-7775-465c-be1c-77030042bde1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_c57b4bca-8275-4675-8ffd-ab1c19f10887" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_79528e7e-0234-47aa-bbce-5a04c9990576" xlink:to="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_c57b4bca-8275-4675-8ffd-ab1c19f10887" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDebtIssuanceCosts_51073e1d-0cea-43a0-a972-c426e69b521f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsOfDebtIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_79528e7e-0234-47aa-bbce-5a04c9990576" xlink:to="loc_us-gaap_PaymentsOfDebtIssuanceCosts_51073e1d-0cea-43a0-a972-c426e69b521f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfSecuredDebt_7db4e0fa-6d47-43af-a86a-0ed9ce82b564" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromIssuanceOfSecuredDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_79528e7e-0234-47aa-bbce-5a04c9990576" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfSecuredDebt_7db4e0fa-6d47-43af-a86a-0ed9ce82b564" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_51a8b659-9fff-4b12-8e33-58fda2704aa5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_79528e7e-0234-47aa-bbce-5a04c9990576" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_51a8b659-9fff-4b12-8e33-58fda2704aa5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLinesOfCredit_fe8a005a-0d81-44f3-a0c3-caed7bfe78f9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RepaymentsOfLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_79528e7e-0234-47aa-bbce-5a04c9990576" xlink:to="loc_us-gaap_RepaymentsOfLinesOfCredit_fe8a005a-0d81-44f3-a0c3-caed7bfe78f9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_8c9ad0e4-778a-4d72-9042-939d2eb65261" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_79528e7e-0234-47aa-bbce-5a04c9990576" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfCommonStock_8c9ad0e4-778a-4d72-9042-939d2eb65261" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfStockIssuanceCosts_082efc96-923d-4034-8d7e-123e954e471d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsOfStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_79528e7e-0234-47aa-bbce-5a04c9990576" xlink:to="loc_us-gaap_PaymentsOfStockIssuanceCosts_082efc96-923d-4034-8d7e-123e954e471d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfRedeemablePreferredStock_f262dbdf-f3aa-4443-8cfc-a23460b7a554" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromIssuanceOfRedeemablePreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_79528e7e-0234-47aa-bbce-5a04c9990576" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfRedeemablePreferredStock_f262dbdf-f3aa-4443-8cfc-a23460b7a554" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRepurchaseOfRedeemableConvertiblePreferredStock_60a78194-6fb8-40f8-af09-1edb7ede1921" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsForRepurchaseOfRedeemableConvertiblePreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_79528e7e-0234-47aa-bbce-5a04c9990576" xlink:to="loc_us-gaap_PaymentsForRepurchaseOfRedeemableConvertiblePreferredStock_60a78194-6fb8-40f8-af09-1edb7ede1921" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_d06dd255-7f7c-464e-9583-515c16c6bedf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_79528e7e-0234-47aa-bbce-5a04c9990576" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_d06dd255-7f7c-464e-9583-515c16c6bedf" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_bb773ef5-d6b6-4ecd-a711-930e14905395" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_58b5ac6f-dd22-4de4-872b-dd30454d8ae7" xlink:to="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsIncludingDisposalGroupAndDiscontinuedOperations_bb773ef5-d6b6-4ecd-a711-930e14905395" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_ee25b23e-7868-4379-9631-380d5b570d8b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_58b5ac6f-dd22-4de4-872b-dd30454d8ae7" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_ee25b23e-7868-4379-9631-380d5b570d8b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_c565c238-17a0-43b6-935c-89d71a28803f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_58b5ac6f-dd22-4de4-872b-dd30454d8ae7" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_c565c238-17a0-43b6-935c-89d71a28803f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_139081e4-811c-4034-92de-4cb1f8b63bbf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_f0d8ac40-276a-4b56-ab63-f1f7f0b433c6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NoncashInvestingAndFinancingItemsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_58b5ac6f-dd22-4de4-872b-dd30454d8ae7" xlink:to="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_f0d8ac40-276a-4b56-ab63-f1f7f0b433c6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPreferredStockPaidinkind_9be48ede-eed8-4b00-a0ed-0f8d7990aea1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DividendsPreferredStockPaidinkind"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NoncashInvestingAndFinancingItemsAbstract_f0d8ac40-276a-4b56-ab63-f1f7f0b433c6" xlink:to="loc_us-gaap_DividendsPreferredStockPaidinkind_9be48ede-eed8-4b00-a0ed-0f8d7990aea1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_5589313e-905d-45de-bb2c-f3a96024015c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_58b5ac6f-dd22-4de4-872b-dd30454d8ae7" xlink:to="loc_us-gaap_StatementTable_5589313e-905d-45de-bb2c-f3a96024015c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_4b619e8f-d0b7-4f9e-abea-451863f8cd6e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_5589313e-905d-45de-bb2c-f3a96024015c" xlink:to="loc_us-gaap_StatementClassOfStockAxis_4b619e8f-d0b7-4f9e-abea-451863f8cd6e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_4b619e8f-d0b7-4f9e-abea-451863f8cd6e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_4b619e8f-d0b7-4f9e-abea-451863f8cd6e" xlink:to="loc_us-gaap_ClassOfStockDomain_4b619e8f-d0b7-4f9e-abea-451863f8cd6e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_87668689-3d50-4737-a416-ff80ba28c44b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_4b619e8f-d0b7-4f9e-abea-451863f8cd6e" xlink:to="loc_us-gaap_ClassOfStockDomain_87668689-3d50-4737-a416-ff80ba28c44b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesBPreferredStockMember_1c997ec5-4ba4-4461-bfca-b864bbc5e563" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SeriesBPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_87668689-3d50-4737-a416-ff80ba28c44b" xlink:to="loc_us-gaap_SeriesBPreferredStockMember_1c997ec5-4ba4-4461-bfca-b864bbc5e563" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUnauditedParenthetical" xlink:type="simple" xlink:href="sncr-20210630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUnauditedParenthetical"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUnauditedParenthetical" xlink:type="extended" id="i68c96a926aa244119d2bdd0aec1fc53c_CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWSUnauditedParenthetical">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_49b50753-7f4f-4328-a0a2-296b47cafb6f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_a2bcf9bc-3070-411b-b18d-a7da011894a4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_49b50753-7f4f-4328-a0a2-296b47cafb6f" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_a2bcf9bc-3070-411b-b18d-a7da011894a4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DeferredStockIssuanceCosts_f36f631f-0279-4f87-82c7-700152244531" xlink:href="sncr-20210630.xsd#sncr_DeferredStockIssuanceCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_49b50753-7f4f-4328-a0a2-296b47cafb6f" xlink:to="loc_sncr_DeferredStockIssuanceCosts_f36f631f-0279-4f87-82c7-700152244531" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_16ac29ec-3cfb-494b-a7cb-2984d35e5c28" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_49b50753-7f4f-4328-a0a2-296b47cafb6f" xlink:to="loc_us-gaap_StatementTable_16ac29ec-3cfb-494b-a7cb-2984d35e5c28" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_fe060b50-2861-4a1e-91d0-05ab7c64cd6f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_16ac29ec-3cfb-494b-a7cb-2984d35e5c28" xlink:to="loc_us-gaap_StatementClassOfStockAxis_fe060b50-2861-4a1e-91d0-05ab7c64cd6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_fe060b50-2861-4a1e-91d0-05ab7c64cd6f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_fe060b50-2861-4a1e-91d0-05ab7c64cd6f" xlink:to="loc_us-gaap_ClassOfStockDomain_fe060b50-2861-4a1e-91d0-05ab7c64cd6f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_2d446b0e-4db6-4666-ac95-c8c11d104ff7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_fe060b50-2861-4a1e-91d0-05ab7c64cd6f" xlink:to="loc_us-gaap_ClassOfStockDomain_2d446b0e-4db6-4666-ac95-c8c11d104ff7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesBPreferredStockMember_99ebf1cf-26f1-4492-833f-3af01d734feb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SeriesBPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_2d446b0e-4db6-4666-ac95-c8c11d104ff7" xlink:to="loc_us-gaap_SeriesBPreferredStockMember_99ebf1cf-26f1-4492-833f-3af01d734feb" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/RevenueDisaggregationofRevenueDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#RevenueDisaggregationofRevenueDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/RevenueDisaggregationofRevenueDetails" xlink:type="extended" id="ib5b7db06234c47568176a5b12fe9e541_RevenueDisaggregationofRevenueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_3d8e9133-88d3-49f8-8de8-e68617ee29b1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_e1f39608-f98e-4862-b184-eb3431d0ba42" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_3d8e9133-88d3-49f8-8de8-e68617ee29b1" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_e1f39608-f98e-4862-b184-eb3431d0ba42" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_6d6b72a5-2538-4da1-a162-bbd6ded0b175" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_3d8e9133-88d3-49f8-8de8-e68617ee29b1" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_6d6b72a5-2538-4da1-a162-bbd6ded0b175" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_20e80f1a-d82f-4102-a9c6-5ea753acb990" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_6d6b72a5-2538-4da1-a162-bbd6ded0b175" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_20e80f1a-d82f-4102-a9c6-5ea753acb990" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_20e80f1a-d82f-4102-a9c6-5ea753acb990_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_20e80f1a-d82f-4102-a9c6-5ea753acb990" xlink:to="loc_us-gaap_SegmentDomain_20e80f1a-d82f-4102-a9c6-5ea753acb990_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_c8903dcc-821f-4155-8046-97d03ca84369" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_20e80f1a-d82f-4102-a9c6-5ea753acb990" xlink:to="loc_us-gaap_SegmentDomain_c8903dcc-821f-4155-8046-97d03ca84369" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_CloudMember_55ed378a-f57e-4ae0-a374-d78a88dcfaba" xlink:href="sncr-20210630.xsd#sncr_CloudMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_c8903dcc-821f-4155-8046-97d03ca84369" xlink:to="loc_sncr_CloudMember_55ed378a-f57e-4ae0-a374-d78a88dcfaba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DigitalMember_6d98dd74-a7e2-4dfa-8d35-031bd024e875" xlink:href="sncr-20210630.xsd#sncr_DigitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_c8903dcc-821f-4155-8046-97d03ca84369" xlink:to="loc_sncr_DigitalMember_6d98dd74-a7e2-4dfa-8d35-031bd024e875" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_MessagingMember_5821e566-fb07-42be-940a-1e6e8f0cedf1" xlink:href="sncr-20210630.xsd#sncr_MessagingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_c8903dcc-821f-4155-8046-97d03ca84369" xlink:to="loc_sncr_MessagingMember_5821e566-fb07-42be-940a-1e6e8f0cedf1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_9dec5cc2-da77-4792-9c32-95ef9ff7b839" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_6d6b72a5-2538-4da1-a162-bbd6ded0b175" xlink:to="loc_srt_StatementGeographicalAxis_9dec5cc2-da77-4792-9c32-95ef9ff7b839" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_9dec5cc2-da77-4792-9c32-95ef9ff7b839_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_9dec5cc2-da77-4792-9c32-95ef9ff7b839" xlink:to="loc_srt_SegmentGeographicalDomain_9dec5cc2-da77-4792-9c32-95ef9ff7b839_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_fdeb4678-43c2-47b7-8fae-a2715d605c86" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_9dec5cc2-da77-4792-9c32-95ef9ff7b839" xlink:to="loc_srt_SegmentGeographicalDomain_fdeb4678-43c2-47b7-8fae-a2715d605c86" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AmericasMember_b3892ab6-9d6f-4b4f-9a14-49604a1e6b71" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_AmericasMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_fdeb4678-43c2-47b7-8fae-a2715d605c86" xlink:to="loc_srt_AmericasMember_b3892ab6-9d6f-4b4f-9a14-49604a1e6b71" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_AsiaPacificMember_fff63364-c71e-4818-81f8-65605cb44b78" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_AsiaPacificMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_fdeb4678-43c2-47b7-8fae-a2715d605c86" xlink:to="loc_srt_AsiaPacificMember_fff63364-c71e-4818-81f8-65605cb44b78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EMEAMember_6e367797-633f-4b1a-8c37-2f6adf4665ec" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EMEAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_fdeb4678-43c2-47b7-8fae-a2715d605c86" xlink:to="loc_us-gaap_EMEAMember_6e367797-633f-4b1a-8c37-2f6adf4665ec" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_10afc8fd-638f-43c7-bb1c-a683c68a0509" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_6d6b72a5-2538-4da1-a162-bbd6ded0b175" xlink:to="loc_srt_ProductOrServiceAxis_10afc8fd-638f-43c7-bb1c-a683c68a0509" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_10afc8fd-638f-43c7-bb1c-a683c68a0509_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_10afc8fd-638f-43c7-bb1c-a683c68a0509" xlink:to="loc_srt_ProductsAndServicesDomain_10afc8fd-638f-43c7-bb1c-a683c68a0509_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_deb1c35c-f9b4-44ce-9342-79ed38a7bbb6" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_10afc8fd-638f-43c7-bb1c-a683c68a0509" xlink:to="loc_srt_ProductsAndServicesDomain_deb1c35c-f9b4-44ce-9342-79ed38a7bbb6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ProfessionalServicesMember_007a3d42-f1a3-4e42-92b1-f8c813071c9f" xlink:href="sncr-20210630.xsd#sncr_ProfessionalServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_deb1c35c-f9b4-44ce-9342-79ed38a7bbb6" xlink:to="loc_sncr_ProfessionalServicesMember_007a3d42-f1a3-4e42-92b1-f8c813071c9f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TransactionServicesMember_2e8c21df-5fff-4d11-93e1-7de4e1f36b36" xlink:href="sncr-20210630.xsd#sncr_TransactionServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_deb1c35c-f9b4-44ce-9342-79ed38a7bbb6" xlink:to="loc_sncr_TransactionServicesMember_2e8c21df-5fff-4d11-93e1-7de4e1f36b36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_SubscriptionServicesMember_a4062df7-ec32-4a23-ae25-ed6ae7f33a9d" xlink:href="sncr-20210630.xsd#sncr_SubscriptionServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_deb1c35c-f9b4-44ce-9342-79ed38a7bbb6" xlink:to="loc_sncr_SubscriptionServicesMember_a4062df7-ec32-4a23-ae25-ed6ae7f33a9d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicenseMember_a1ecc62d-f540-4c67-8191-91e726dfe7b5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_deb1c35c-f9b4-44ce-9342-79ed38a7bbb6" xlink:to="loc_us-gaap_LicenseMember_a1ecc62d-f540-4c67-8191-91e726dfe7b5" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/RevenueRemainingPerformanceObligationsDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#RevenueRemainingPerformanceObligationsDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/RevenueRemainingPerformanceObligationsDetails" xlink:type="extended" id="ia9ba4cd8e7d24c05b07a405ba02da153_RevenueRemainingPerformanceObligationsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_7c1094e9-8567-4d4d-90e3-f693cecdcc6d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_3d308384-dea3-426f-a1ec-8a4929bdc35d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_7c1094e9-8567-4d4d-90e3-f693cecdcc6d" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_3d308384-dea3-426f-a1ec-8a4929bdc35d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_5d3f353c-c9e4-4552-badf-9abe5744222a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_7c1094e9-8567-4d4d-90e3-f693cecdcc6d" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_5d3f353c-c9e4-4552-badf-9abe5744222a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_db9477ac-7e32-4728-9200-ed58c6ae68ec" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_7c1094e9-8567-4d4d-90e3-f693cecdcc6d" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_db9477ac-7e32-4728-9200-ed58c6ae68ec" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_bb1840b0-ca34-4798-bbf2-7bed5b81152c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_7c1094e9-8567-4d4d-90e3-f693cecdcc6d" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_bb1840b0-ca34-4798-bbf2-7bed5b81152c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_d88d5658-fc79-48a8-9c71-ad9ed149e823" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_bb1840b0-ca34-4798-bbf2-7bed5b81152c" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_d88d5658-fc79-48a8-9c71-ad9ed149e823" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/RevenueRemainingPerformanceObligationsDetails_1" xlink:type="simple" xlink:href="sncr-20210630.xsd#RevenueRemainingPerformanceObligationsDetails_1"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/RevenueRemainingPerformanceObligationsDetails_1" xlink:type="extended" id="if843d397004f49f4a0bf490da145af63_RevenueRemainingPerformanceObligationsDetails_1">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_7c1094e9-8567-4d4d-90e3-f693cecdcc6d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_3d308384-dea3-426f-a1ec-8a4929bdc35d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_7c1094e9-8567-4d4d-90e3-f693cecdcc6d" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_3d308384-dea3-426f-a1ec-8a4929bdc35d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_5d3f353c-c9e4-4552-badf-9abe5744222a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_7c1094e9-8567-4d4d-90e3-f693cecdcc6d" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_5d3f353c-c9e4-4552-badf-9abe5744222a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_db9477ac-7e32-4728-9200-ed58c6ae68ec" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_7c1094e9-8567-4d4d-90e3-f693cecdcc6d" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_db9477ac-7e32-4728-9200-ed58c6ae68ec" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_bb1840b0-ca34-4798-bbf2-7bed5b81152c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_7c1094e9-8567-4d4d-90e3-f693cecdcc6d" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_bb1840b0-ca34-4798-bbf2-7bed5b81152c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/FairValueMeasurementsHierarchyDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#FairValueMeasurementsHierarchyDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/FairValueMeasurementsHierarchyDetails" xlink:type="extended" id="id0b5d9cb5b1f45cd946f7ae408b5a036_FairValueMeasurementsHierarchyDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6555e4d1-8a7f-402c-9f0e-965d5b8c1443" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_3fd18adc-dc0d-4a31-a77f-c4783b133e13" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6555e4d1-8a7f-402c-9f0e-965d5b8c1443" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_3fd18adc-dc0d-4a31-a77f-c4783b133e13" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_3e0f6bfe-edce-4a6d-9281-8fdff26560b2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_3fd18adc-dc0d-4a31-a77f-c4783b133e13" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_3e0f6bfe-edce-4a6d-9281-8fdff26560b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_3fa7c24a-ea8f-4283-9c41-43baba31e089" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_3fd18adc-dc0d-4a31-a77f-c4783b133e13" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_3fa7c24a-ea8f-4283-9c41-43baba31e089" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityFairValueDisclosureAbstract_56035a15-cd37-473b-af96-b8c223f42ddd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6555e4d1-8a7f-402c-9f0e-965d5b8c1443" xlink:to="loc_us-gaap_EquityFairValueDisclosureAbstract_56035a15-cd37-473b-af96-b8c223f42ddd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityOtherFairValue_231d2317-2d84-4f1b-85ea-86a9d5870e6c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RedeemableNoncontrollingInterestEquityOtherFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityFairValueDisclosureAbstract_56035a15-cd37-473b-af96-b8c223f42ddd" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityOtherFairValue_231d2317-2d84-4f1b-85ea-86a9d5870e6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityFairValueDisclosure_858324b0-abe5-4074-b332-180fd61b12b2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityFairValueDisclosureAbstract_56035a15-cd37-473b-af96-b8c223f42ddd" xlink:to="loc_us-gaap_EquityFairValueDisclosure_858324b0-abe5-4074-b332-180fd61b12b2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7a591452-50ab-4fc4-886b-c921f110bf6d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6555e4d1-8a7f-402c-9f0e-965d5b8c1443" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7a591452-50ab-4fc4-886b-c921f110bf6d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_7732b81d-4765-46e6-946d-4d88e81d29ee" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_7a591452-50ab-4fc4-886b-c921f110bf6d" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_7732b81d-4765-46e6-946d-4d88e81d29ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7732b81d-4765-46e6-946d-4d88e81d29ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_7732b81d-4765-46e6-946d-4d88e81d29ee" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_7732b81d-4765-46e6-946d-4d88e81d29ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_fe913eee-a518-4e4a-9b3f-90569f88eb40" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_7732b81d-4765-46e6-946d-4d88e81d29ee" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_fe913eee-a518-4e4a-9b3f-90569f88eb40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_ec2bbd75-4791-42c1-84ab-5c8ac8ce951b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_fe913eee-a518-4e4a-9b3f-90569f88eb40" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_ec2bbd75-4791-42c1-84ab-5c8ac8ce951b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_eef6947a-6a13-4f35-8bd2-8df9addacf52" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_fe913eee-a518-4e4a-9b3f-90569f88eb40" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_eef6947a-6a13-4f35-8bd2-8df9addacf52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_32e7a976-c406-43dc-b9c5-f91c8375e1c2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_fe913eee-a518-4e4a-9b3f-90569f88eb40" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_32e7a976-c406-43dc-b9c5-f91c8375e1c2" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/FairValueMeasurementsLevel3RedeemableNoncontrollingInterestsDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#FairValueMeasurementsLevel3RedeemableNoncontrollingInterestsDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/FairValueMeasurementsLevel3RedeemableNoncontrollingInterestsDetails" xlink:type="extended" id="i766948d110c24af8ae82087563a20919_FairValueMeasurementsLevel3RedeemableNoncontrollingInterestsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_e2e41ff5-2b39-41f5-b367-b98fdb725307" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward_63bcfff9-adba-43c3-9d60-041cbe3354e6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_e2e41ff5-2b39-41f5-b367-b98fdb725307" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward_63bcfff9-adba-43c3-9d60-041cbe3354e6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs_0d10cde1-af1b-420f-b931-2b16e495f975" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward_63bcfff9-adba-43c3-9d60-041cbe3354e6" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs_0d10cde1-af1b-420f-b931-2b16e495f975" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityAccretionToRedemptionValue_af6bfee1-7052-409d-9a9c-daeba3f279da" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityAccretionToRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward_63bcfff9-adba-43c3-9d60-041cbe3354e6" xlink:to="loc_us-gaap_TemporaryEquityAccretionToRedemptionValue_af6bfee1-7052-409d-9a9c-daeba3f279da" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationGainLossIncludedInEarnings_45fd6a60-70b3-4570-9fc3-8d1c85ef9121" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward_63bcfff9-adba-43c3-9d60-041cbe3354e6" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationGainLossIncludedInEarnings_45fd6a60-70b3-4570-9fc3-8d1c85ef9121" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs_6e0d59b7-4367-497c-bf9d-dc3febe3fb94" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTable_32964de5-24fc-4461-8f50-eb15700a1657" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_e2e41ff5-2b39-41f5-b367-b98fdb725307" xlink:to="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTable_32964de5-24fc-4461-8f50-eb15700a1657" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_eb81a403-2ea9-423c-936f-23912c816382" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationTable_32964de5-24fc-4461-8f50-eb15700a1657" xlink:to="loc_dei_LegalEntityAxis_eb81a403-2ea9-423c-936f-23912c816382" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_eb81a403-2ea9-423c-936f-23912c816382_default" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_eb81a403-2ea9-423c-936f-23912c816382" xlink:to="loc_dei_EntityDomain_eb81a403-2ea9-423c-936f-23912c816382_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_95473d8e-da68-4f51-8b68-1aa3095b8dc1" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_eb81a403-2ea9-423c-936f-23912c816382" xlink:to="loc_dei_EntityDomain_95473d8e-da68-4f51-8b68-1aa3095b8dc1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_RedeemableNoncontrollingInterestMember_faa52b5f-da62-4101-87f2-4a91e021aa9c" xlink:href="sncr-20210630.xsd#sncr_RedeemableNoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_95473d8e-da68-4f51-8b68-1aa3095b8dc1" xlink:to="loc_sncr_RedeemableNoncontrollingInterestMember_faa52b5f-da62-4101-87f2-4a91e021aa9c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/InvestmentsinAffiliatesandRelatedTransactionsDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#InvestmentsinAffiliatesandRelatedTransactionsDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/InvestmentsinAffiliatesandRelatedTransactionsDetails" xlink:type="extended" id="i4721c2a9431345788fa092deb77ba157_InvestmentsinAffiliatesandRelatedTransactionsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_cbb81343-49a1-467a-afee-24f825556212" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DurationofCustomerContract_25b88e86-38e2-48d0-8c03-facacd32dd27" xlink:href="sncr-20210630.xsd#sncr_DurationofCustomerContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_cbb81343-49a1-467a-afee-24f825556212" xlink:to="loc_sncr_DurationofCustomerContract_25b88e86-38e2-48d0-8c03-facacd32dd27" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_AssetPurchaseAgreementConsiderationReceived_98038ff2-0f03-4d3c-9399-fbf0169adcce" xlink:href="sncr-20210630.xsd#sncr_AssetPurchaseAgreementConsiderationReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_cbb81343-49a1-467a-afee-24f825556212" xlink:to="loc_sncr_AssetPurchaseAgreementConsiderationReceived_98038ff2-0f03-4d3c-9399-fbf0169adcce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_595c983b-5325-46b4-bad6-0e6816a8d74a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_cbb81343-49a1-467a-afee-24f825556212" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_595c983b-5325-46b4-bad6-0e6816a8d74a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentContingentConsiderationLiability_ca53d360-c1cc-4143-8db7-99db2cd18b58" xlink:href="sncr-20210630.xsd#sncr_DebtInstrumentContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_cbb81343-49a1-467a-afee-24f825556212" xlink:to="loc_sncr_DebtInstrumentContingentConsiderationLiability_ca53d360-c1cc-4143-8db7-99db2cd18b58" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_8e5ee128-18b5-4957-8b71-2f2583dc7afe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_cbb81343-49a1-467a-afee-24f825556212" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_8e5ee128-18b5-4957-8b71-2f2583dc7afe" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTerm_0195c6bb-414e-4afe-bd8b-090cb245878e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_cbb81343-49a1-467a-afee-24f825556212" xlink:to="loc_us-gaap_DebtInstrumentTerm_0195c6bb-414e-4afe-bd8b-090cb245878e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentProceedsFromSalePercentage_1602fd0d-6f98-4c55-acef-6793205dd0fc" xlink:href="sncr-20210630.xsd#sncr_DebtInstrumentProceedsFromSalePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_cbb81343-49a1-467a-afee-24f825556212" xlink:to="loc_sncr_DebtInstrumentProceedsFromSalePercentage_1602fd0d-6f98-4c55-acef-6793205dd0fc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsFairValueDisclosure_56b878c7-bbfb-412e-a0c6-e9416a2f218a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherAssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_cbb81343-49a1-467a-afee-24f825556212" xlink:to="loc_us-gaap_OtherAssetsFairValueDisclosure_56b878c7-bbfb-412e-a0c6-e9416a2f218a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_270920c5-c6f4-43d6-8c6a-e8c68763f31a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsLineItems_cbb81343-49a1-467a-afee-24f825556212" xlink:to="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_270920c5-c6f4-43d6-8c6a-e8c68763f31a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_88db1d2f-96e6-44b1-bc5a-6a70ba85c3b6" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_270920c5-c6f4-43d6-8c6a-e8c68763f31a" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_88db1d2f-96e6-44b1-bc5a-6a70ba85c3b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_88db1d2f-96e6-44b1-bc5a-6a70ba85c3b6_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_88db1d2f-96e6-44b1-bc5a-6a70ba85c3b6" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_88db1d2f-96e6-44b1-bc5a-6a70ba85c3b6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_100688d6-f9d3-4d3a-a7f4-10d4dc8a880b" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_88db1d2f-96e6-44b1-bc5a-6a70ba85c3b6" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_100688d6-f9d3-4d3a-a7f4-10d4dc8a880b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_SequentialTechnologyInternationalLLCMember_af0745bb-8513-4f74-8848-6c3fbb0b8974" xlink:href="sncr-20210630.xsd#sncr_SequentialTechnologyInternationalLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_100688d6-f9d3-4d3a-a7f4-10d4dc8a880b" xlink:to="loc_sncr_SequentialTechnologyInternationalLLCMember_af0745bb-8513-4f74-8848-6c3fbb0b8974" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_6105aa4e-2a97-4fa0-9caa-586ae873c1bd" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_270920c5-c6f4-43d6-8c6a-e8c68763f31a" xlink:to="loc_srt_CounterpartyNameAxis_6105aa4e-2a97-4fa0-9caa-586ae873c1bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_6105aa4e-2a97-4fa0-9caa-586ae873c1bd_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_6105aa4e-2a97-4fa0-9caa-586ae873c1bd" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_6105aa4e-2a97-4fa0-9caa-586ae873c1bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_ce20d011-df60-4ec0-b249-32cf569b559a" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_6105aa4e-2a97-4fa0-9caa-586ae873c1bd" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_ce20d011-df60-4ec0-b249-32cf569b559a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_SequentialTechnologyInternationalLLCAndAPCapitalHoldingsIILLCMember_06ba35aa-33d0-48ee-908c-5791ed321f48" xlink:href="sncr-20210630.xsd#sncr_SequentialTechnologyInternationalLLCAndAPCapitalHoldingsIILLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_ce20d011-df60-4ec0-b249-32cf569b559a" xlink:to="loc_sncr_SequentialTechnologyInternationalLLCAndAPCapitalHoldingsIILLCMember_06ba35aa-33d0-48ee-908c-5791ed321f48" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_274588ec-cf91-4f90-ae68-570064e7b1c8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEquityMethodInvestmentsTable_270920c5-c6f4-43d6-8c6a-e8c68763f31a" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_274588ec-cf91-4f90-ae68-570064e7b1c8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_274588ec-cf91-4f90-ae68-570064e7b1c8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_274588ec-cf91-4f90-ae68-570064e7b1c8" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_274588ec-cf91-4f90-ae68-570064e7b1c8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_ffc273fe-80be-4842-b903-5735eac155ef" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_274588ec-cf91-4f90-ae68-570064e7b1c8" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_ffc273fe-80be-4842-b903-5735eac155ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LoansPayableMember_50744ac2-15f3-4fd1-892f-98b074d99aea" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LoansPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_ffc273fe-80be-4842-b903-5735eac155ef" xlink:to="loc_us-gaap_LoansPayableMember_50744ac2-15f3-4fd1-892f-98b074d99aea" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/DebtOfferingofSeniorNotesDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#DebtOfferingofSeniorNotesDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/DebtOfferingofSeniorNotesDetails" xlink:type="extended" id="i44bd74afd8204262a56768d64e94cd9b_DebtOfferingofSeniorNotesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_bc8b2017-ef23-4a34-ab6b-bb1f4d154821" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_4d883a28-d901-43be-ab33-be6b61a0890d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bc8b2017-ef23-4a34-ab6b-bb1f4d154821" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_4d883a28-d901-43be-ab33-be6b61a0890d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentParValue_f5a4910d-8091-4ceb-a4cc-65557b3c8a48" xlink:href="sncr-20210630.xsd#sncr_DebtInstrumentParValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bc8b2017-ef23-4a34-ab6b-bb1f4d154821" xlink:to="loc_sncr_DebtInstrumentParValue_f5a4910d-8091-4ceb-a4cc-65557b3c8a48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_b03421dd-833a-4ffc-90e1-bbba7dc19b16" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bc8b2017-ef23-4a34-ab6b-bb1f4d154821" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_b03421dd-833a-4ffc-90e1-bbba7dc19b16" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentFaceAmountInclusiveOfUnderwritersOptionToPurchase_9144a9db-f821-4210-aaa2-29788919b710" xlink:href="sncr-20210630.xsd#sncr_DebtInstrumentFaceAmountInclusiveOfUnderwritersOptionToPurchase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bc8b2017-ef23-4a34-ab6b-bb1f4d154821" xlink:to="loc_sncr_DebtInstrumentFaceAmountInclusiveOfUnderwritersOptionToPurchase_9144a9db-f821-4210-aaa2-29788919b710" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentUnderwritersOptionToPurchase_c6514280-73ab-49b7-996d-099072e8571e" xlink:href="sncr-20210630.xsd#sncr_DebtInstrumentUnderwritersOptionToPurchase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bc8b2017-ef23-4a34-ab6b-bb1f4d154821" xlink:to="loc_sncr_DebtInstrumentUnderwritersOptionToPurchase_c6514280-73ab-49b7-996d-099072e8571e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentRedemptionPrice_854037c9-23f7-4b5e-afb7-469f0ce8d71d" xlink:href="sncr-20210630.xsd#sncr_DebtInstrumentRedemptionPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bc8b2017-ef23-4a34-ab6b-bb1f4d154821" xlink:to="loc_sncr_DebtInstrumentRedemptionPrice_854037c9-23f7-4b5e-afb7-469f0ce8d71d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_130bb3a2-ed6f-4a50-8d1a-b3959ad458ef" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bc8b2017-ef23-4a34-ab6b-bb1f4d154821" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_130bb3a2-ed6f-4a50-8d1a-b3959ad458ef" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentPercentageOfDebtHoldersDemandFullRepaymentOnDebtDefaultAmount_8ab18f6b-3f67-4b77-8c2f-80a90115ede0" xlink:href="sncr-20210630.xsd#sncr_DebtInstrumentPercentageOfDebtHoldersDemandFullRepaymentOnDebtDefaultAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bc8b2017-ef23-4a34-ab6b-bb1f4d154821" xlink:to="loc_sncr_DebtInstrumentPercentageOfDebtHoldersDemandFullRepaymentOnDebtDefaultAmount_8ab18f6b-3f67-4b77-8c2f-80a90115ede0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_ea1ec170-913e-4124-b275-ae29000e4d8a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_bc8b2017-ef23-4a34-ab6b-bb1f4d154821" xlink:to="loc_us-gaap_DebtInstrumentTable_ea1ec170-913e-4124-b275-ae29000e4d8a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_3cd7b713-3522-4838-ab59-aaf3423db2df" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_ea1ec170-913e-4124-b275-ae29000e4d8a" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_3cd7b713-3522-4838-ab59-aaf3423db2df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_3cd7b713-3522-4838-ab59-aaf3423db2df_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_3cd7b713-3522-4838-ab59-aaf3423db2df" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_3cd7b713-3522-4838-ab59-aaf3423db2df_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_f6f41f7c-d661-47d8-876f-9b96ed94a104" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_3cd7b713-3522-4838-ab59-aaf3423db2df" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_f6f41f7c-d661-47d8-876f-9b96ed94a104" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_23b80790-f42b-4f2a-8a20-45ab8483321e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_f6f41f7c-d661-47d8-876f-9b96ed94a104" xlink:to="loc_us-gaap_SeniorNotesMember_23b80790-f42b-4f2a-8a20-45ab8483321e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_b890af84-0f34-4843-a91f-1d4fd6d76616" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_ea1ec170-913e-4124-b275-ae29000e4d8a" xlink:to="loc_us-gaap_DebtInstrumentAxis_b890af84-0f34-4843-a91f-1d4fd6d76616" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_b890af84-0f34-4843-a91f-1d4fd6d76616_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_b890af84-0f34-4843-a91f-1d4fd6d76616" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_b890af84-0f34-4843-a91f-1d4fd6d76616_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_c19ed072-17aa-498b-98e5-7592a9ea022b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_b890af84-0f34-4843-a91f-1d4fd6d76616" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_c19ed072-17aa-498b-98e5-7592a9ea022b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_SeniorNotesDueJune302026Member_bfa56682-ac9f-4476-a962-b49afc56d432" xlink:href="sncr-20210630.xsd#sncr_SeniorNotesDueJune302026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_c19ed072-17aa-498b-98e5-7592a9ea022b" xlink:to="loc_sncr_SeniorNotesDueJune302026Member_bfa56682-ac9f-4476-a962-b49afc56d432" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_57743467-b985-42cd-bf8f-69a1cc8ebd13" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_ea1ec170-913e-4124-b275-ae29000e4d8a" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_57743467-b985-42cd-bf8f-69a1cc8ebd13" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_57743467-b985-42cd-bf8f-69a1cc8ebd13_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_57743467-b985-42cd-bf8f-69a1cc8ebd13" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_57743467-b985-42cd-bf8f-69a1cc8ebd13_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_38b8c00b-f567-45c5-a018-cd13c3987c87" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_57743467-b985-42cd-bf8f-69a1cc8ebd13" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_38b8c00b-f567-45c5-a018-cd13c3987c87" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_bfd65115-edc4-4a78-9982-f2535edcd149" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_38b8c00b-f567-45c5-a018-cd13c3987c87" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_bfd65115-edc4-4a78-9982-f2535edcd149" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodTwoMember_943147c2-da82-4d64-8da8-d47f338fbdb4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_38b8c00b-f567-45c5-a018-cd13c3987c87" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodTwoMember_943147c2-da82-4d64-8da8-d47f338fbdb4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodThreeMember_ebf4697d-3cc7-4c04-9a37-72ddaab1e8b6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_38b8c00b-f567-45c5-a018-cd13c3987c87" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodThreeMember_ebf4697d-3cc7-4c04-9a37-72ddaab1e8b6" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/DebtCarryingAmountsDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#DebtCarryingAmountsDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/DebtCarryingAmountsDetails" xlink:type="extended" id="ic283a3f731f24b6ab41804fc20a3fb9b_DebtCarryingAmountsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_a7eff0ac-5959-45d0-a86f-cdbda202ce52" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_007a8009-8780-4614-bc6c-d79f938918a1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a7eff0ac-5959-45d0-a86f-cdbda202ce52" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_007a8009-8780-4614-bc6c-d79f938918a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_a36272c9-c2e8-49b9-b8ae-fd407a56ffb8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a7eff0ac-5959-45d0-a86f-cdbda202ce52" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_a36272c9-c2e8-49b9-b8ae-fd407a56ffb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_14da5d99-eefc-4d60-8949-0b5b46fd0202" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a7eff0ac-5959-45d0-a86f-cdbda202ce52" xlink:to="loc_us-gaap_LongTermDebt_14da5d99-eefc-4d60-8949-0b5b46fd0202" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_60d102f0-5392-4d73-b74b-afbcc9fe896e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a7eff0ac-5959-45d0-a86f-cdbda202ce52" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_60d102f0-5392-4d73-b74b-afbcc9fe896e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_d8a2d997-a4bd-4028-bbe0-43fd79645b44" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_a7eff0ac-5959-45d0-a86f-cdbda202ce52" xlink:to="loc_us-gaap_DebtInstrumentTable_d8a2d997-a4bd-4028-bbe0-43fd79645b44" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_3d20844e-e841-4a52-a6ca-eb956f5abc92" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_d8a2d997-a4bd-4028-bbe0-43fd79645b44" xlink:to="loc_us-gaap_DebtInstrumentAxis_3d20844e-e841-4a52-a6ca-eb956f5abc92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_3d20844e-e841-4a52-a6ca-eb956f5abc92_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_3d20844e-e841-4a52-a6ca-eb956f5abc92" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_3d20844e-e841-4a52-a6ca-eb956f5abc92_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_f01b74dd-bcd1-4bb2-8cfb-41fbbab8b8cf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_3d20844e-e841-4a52-a6ca-eb956f5abc92" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_f01b74dd-bcd1-4bb2-8cfb-41fbbab8b8cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_SeniorNotesDueJune302026Member_0c50167b-f248-41d2-a27e-fd151c3625a0" xlink:href="sncr-20210630.xsd#sncr_SeniorNotesDueJune302026Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_f01b74dd-bcd1-4bb2-8cfb-41fbbab8b8cf" xlink:to="loc_sncr_SeniorNotesDueJune302026Member_0c50167b-f248-41d2-a27e-fd151c3625a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_02b57f21-0d7f-41da-b94b-49a94af3c3d0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_d8a2d997-a4bd-4028-bbe0-43fd79645b44" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_02b57f21-0d7f-41da-b94b-49a94af3c3d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_02b57f21-0d7f-41da-b94b-49a94af3c3d0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_02b57f21-0d7f-41da-b94b-49a94af3c3d0" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_02b57f21-0d7f-41da-b94b-49a94af3c3d0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_4cacb80f-9187-475d-8e6d-4a1d55752a21" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_02b57f21-0d7f-41da-b94b-49a94af3c3d0" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_4cacb80f-9187-475d-8e6d-4a1d55752a21" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_9e473e75-73aa-4d54-83d7-0d0c579cab34" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_4cacb80f-9187-475d-8e6d-4a1d55752a21" xlink:to="loc_us-gaap_SeniorNotesMember_9e473e75-73aa-4d54-83d7-0d0c579cab34" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/Debt2019RevolvingCreditFacilityDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#Debt2019RevolvingCreditFacilityDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/Debt2019RevolvingCreditFacilityDetails" xlink:type="extended" id="i3bfdf4dc42df4800813d87c3c7539817_Debt2019RevolvingCreditFacilityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_a0dbede8-ef5f-4ee5-a8d1-3576bb8ce4a7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_2b717260-a97f-4a62-a470-e58a4945916b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_a0dbede8-ef5f-4ee5-a8d1-3576bb8ce4a7" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_2b717260-a97f-4a62-a470-e58a4945916b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_dfe09ea8-2d22-414c-8f4d-856bfdce7b6e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_a0dbede8-ef5f-4ee5-a8d1-3576bb8ce4a7" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_dfe09ea8-2d22-414c-8f4d-856bfdce7b6e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtFloorInterestRate_32f44fe2-ccb9-4725-85f6-c59fdd13faf5" xlink:href="sncr-20210630.xsd#sncr_DebtFloorInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_a0dbede8-ef5f-4ee5-a8d1-3576bb8ce4a7" xlink:to="loc_sncr_DebtFloorInterestRate_32f44fe2-ccb9-4725-85f6-c59fdd13faf5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_ac080d20-a844-4f64-8e86-8a878e68172a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_a0dbede8-ef5f-4ee5-a8d1-3576bb8ce4a7" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_ac080d20-a844-4f64-8e86-8a878e68172a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_413539ef-b5f1-4428-8f67-534f0d6f0c82" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_ac080d20-a844-4f64-8e86-8a878e68172a" xlink:to="loc_us-gaap_CreditFacilityAxis_413539ef-b5f1-4428-8f67-534f0d6f0c82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_413539ef-b5f1-4428-8f67-534f0d6f0c82_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_413539ef-b5f1-4428-8f67-534f0d6f0c82" xlink:to="loc_us-gaap_CreditFacilityDomain_413539ef-b5f1-4428-8f67-534f0d6f0c82_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_afd75db5-c2fc-48a1-8f9d-7db234abc74f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_413539ef-b5f1-4428-8f67-534f0d6f0c82" xlink:to="loc_us-gaap_CreditFacilityDomain_afd75db5-c2fc-48a1-8f9d-7db234abc74f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_80b6c777-5987-4e30-8bfd-26e07b0fb773" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_afd75db5-c2fc-48a1-8f9d-7db234abc74f" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_80b6c777-5987-4e30-8bfd-26e07b0fb773" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_2fe7e068-8125-4601-84c6-dfa67a844122" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_ac080d20-a844-4f64-8e86-8a878e68172a" xlink:to="loc_us-gaap_VariableRateAxis_2fe7e068-8125-4601-84c6-dfa67a844122" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_2fe7e068-8125-4601-84c6-dfa67a844122_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_2fe7e068-8125-4601-84c6-dfa67a844122" xlink:to="loc_us-gaap_VariableRateDomain_2fe7e068-8125-4601-84c6-dfa67a844122_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_3d1d4966-64f1-4a25-85f2-c1c5395f2df5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_2fe7e068-8125-4601-84c6-dfa67a844122" xlink:to="loc_us-gaap_VariableRateDomain_3d1d4966-64f1-4a25-85f2-c1c5395f2df5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FederalFundsEffectiveSwapRateMember_4291a92e-b973-48bc-80f4-03b10e0d0ece" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FederalFundsEffectiveSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_3d1d4966-64f1-4a25-85f2-c1c5395f2df5" xlink:to="loc_us-gaap_FederalFundsEffectiveSwapRateMember_4291a92e-b973-48bc-80f4-03b10e0d0ece" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_e2d93aca-fdf7-4717-98af-9953f3e2932a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LondonInterbankOfferedRateLIBORMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_3d1d4966-64f1-4a25-85f2-c1c5395f2df5" xlink:to="loc_us-gaap_LondonInterbankOfferedRateLIBORMember_e2d93aca-fdf7-4717-98af-9953f3e2932a" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/DebtInterestExpenseDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#DebtInterestExpenseDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/DebtInterestExpenseDetails" xlink:type="extended" id="i1de9b598f3fd4e8c9a6770b481f98b51_DebtInterestExpenseDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_e34c7f81-b5e0-423e-925d-04161bcd9486" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_fb732e23-2474-4bb6-9ac1-f31f8babf938" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_e34c7f81-b5e0-423e-925d-04161bcd9486" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_fb732e23-2474-4bb6-9ac1-f31f8babf938" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnusedBorrowingCapacityFee_0c9e77d1-b354-4928-bb8a-a54db53209bc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentUnusedBorrowingCapacityFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_e34c7f81-b5e0-423e-925d-04161bcd9486" xlink:to="loc_us-gaap_DebtInstrumentUnusedBorrowingCapacityFee_0c9e77d1-b354-4928-bb8a-a54db53209bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_20eca9a7-6edd-48d3-bb32-783342006ce1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_e34c7f81-b5e0-423e-925d-04161bcd9486" xlink:to="loc_us-gaap_InterestExpenseDebt_20eca9a7-6edd-48d3-bb32-783342006ce1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseOther_7aabfc81-2025-4690-a833-b104c0497951" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestExpenseOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_e34c7f81-b5e0-423e-925d-04161bcd9486" xlink:to="loc_us-gaap_InterestExpenseOther_7aabfc81-2025-4690-a833-b104c0497951" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_58ab81e0-1b66-433f-a058-2bd495bfe5f4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_e34c7f81-b5e0-423e-925d-04161bcd9486" xlink:to="loc_us-gaap_InterestExpense_58ab81e0-1b66-433f-a058-2bd495bfe5f4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_6499cc9c-718e-434c-a567-c946ecaf8f36" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_e34c7f81-b5e0-423e-925d-04161bcd9486" xlink:to="loc_us-gaap_DebtInstrumentTable_6499cc9c-718e-434c-a567-c946ecaf8f36" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_69b1c8f0-87b5-4b1c-a878-3cc548f904a8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_6499cc9c-718e-434c-a567-c946ecaf8f36" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_69b1c8f0-87b5-4b1c-a878-3cc548f904a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_69b1c8f0-87b5-4b1c-a878-3cc548f904a8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_69b1c8f0-87b5-4b1c-a878-3cc548f904a8" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_69b1c8f0-87b5-4b1c-a878-3cc548f904a8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_9c8a9091-6e62-415c-8460-e34027f6defb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_69b1c8f0-87b5-4b1c-a878-3cc548f904a8" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_9c8a9091-6e62-415c-8460-e34027f6defb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_1d77bf27-e5a1-49be-8183-48f8b4fcde57" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_9c8a9091-6e62-415c-8460-e34027f6defb" xlink:to="loc_us-gaap_LineOfCreditMember_1d77bf27-e5a1-49be-8183-48f8b4fcde57" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_d69eecf4-014c-464e-9ce1-76a57ec92aed" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_6499cc9c-718e-434c-a567-c946ecaf8f36" xlink:to="loc_us-gaap_CreditFacilityAxis_d69eecf4-014c-464e-9ce1-76a57ec92aed" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_d69eecf4-014c-464e-9ce1-76a57ec92aed_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_d69eecf4-014c-464e-9ce1-76a57ec92aed" xlink:to="loc_us-gaap_CreditFacilityDomain_d69eecf4-014c-464e-9ce1-76a57ec92aed_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_638ec5ed-974d-4f79-a71c-ce4f63078da3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_d69eecf4-014c-464e-9ce1-76a57ec92aed" xlink:to="loc_us-gaap_CreditFacilityDomain_638ec5ed-974d-4f79-a71c-ce4f63078da3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_96966ad2-134e-4588-9ec6-13812f0de221" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_638ec5ed-974d-4f79-a71c-ce4f63078da3" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_96966ad2-134e-4588-9ec6-13812f0de221" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/AccumulatedOtherComprehensiveLossIncomeDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#AccumulatedOtherComprehensiveLossIncomeDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/AccumulatedOtherComprehensiveLossIncomeDetails" xlink:type="extended" id="i66b22676006943feb9ba45902c2102e0_AccumulatedOtherComprehensiveLossIncomeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_3730b8f1-b992-4fb5-b87b-8a2640679981" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_f24e431d-9e78-439a-b831-b4f3a9936a6f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AOCIAttributableToParentNetOfTaxRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_3730b8f1-b992-4fb5-b87b-8a2640679981" xlink:to="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_f24e431d-9e78-439a-b831-b4f3a9936a6f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_ae2cfe66-10d3-46ee-b0b3-be70e05c66a8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_f24e431d-9e78-439a-b831-b4f3a9936a6f" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_ae2cfe66-10d3-46ee-b0b3-be70e05c66a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTax_a8e77b6e-9517-4743-aefb-fbf853a8ce65" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_f24e431d-9e78-439a-b831-b4f3a9936a6f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeTax_a8e77b6e-9517-4743-aefb-fbf853a8ce65" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossTax_5b15156f-5b91-4d0f-90cf-c2474c7b51bc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_f24e431d-9e78-439a-b831-b4f3a9936a6f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossTax_5b15156f-5b91-4d0f-90cf-c2474c7b51bc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_0c6b6366-be07-4201-abd4-d8cd25cbe32b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_7de585e9-53be-4373-a809-32bcbaf14f15" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_3730b8f1-b992-4fb5-b87b-8a2640679981" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_7de585e9-53be-4373-a809-32bcbaf14f15" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_15441060-e774-4115-8bb9-30a41c6fb804" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_7de585e9-53be-4373-a809-32bcbaf14f15" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_15441060-e774-4115-8bb9-30a41c6fb804" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_15441060-e774-4115-8bb9-30a41c6fb804_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_15441060-e774-4115-8bb9-30a41c6fb804" xlink:to="loc_us-gaap_EquityComponentDomain_15441060-e774-4115-8bb9-30a41c6fb804_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_8684605e-6a4e-4cca-885c-9aeb1e63da73" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_15441060-e774-4115-8bb9-30a41c6fb804" xlink:to="loc_us-gaap_EquityComponentDomain_8684605e-6a4e-4cca-885c-9aeb1e63da73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AociIncludingPortionAttributableToNoncontrollingInterestMember_2dbd9854-68e0-48f0-8ec9-78dc6e46792f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AociIncludingPortionAttributableToNoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_8684605e-6a4e-4cca-885c-9aeb1e63da73" xlink:to="loc_us-gaap_AociIncludingPortionAttributableToNoncontrollingInterestMember_2dbd9854-68e0-48f0-8ec9-78dc6e46792f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedForeignCurrencyAdjustmentIncludingPortionAttributableToNoncontrollingInterestMember_9d5ba69b-45fe-4f4b-9206-27f244e84dfd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedForeignCurrencyAdjustmentIncludingPortionAttributableToNoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AociIncludingPortionAttributableToNoncontrollingInterestMember_2dbd9854-68e0-48f0-8ec9-78dc6e46792f" xlink:to="loc_us-gaap_AccumulatedForeignCurrencyAdjustmentIncludingPortionAttributableToNoncontrollingInterestMember_9d5ba69b-45fe-4f4b-9206-27f244e84dfd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_AccumulatedNetGainLossOnIntraEntityForeignCurrencyTransactionsMember_1d9db660-1f38-4c87-ad19-d250cffe1ace" xlink:href="sncr-20210630.xsd#sncr_AccumulatedNetGainLossOnIntraEntityForeignCurrencyTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AociIncludingPortionAttributableToNoncontrollingInterestMember_2dbd9854-68e0-48f0-8ec9-78dc6e46792f" xlink:to="loc_sncr_AccumulatedNetGainLossOnIntraEntityForeignCurrencyTransactionsMember_1d9db660-1f38-4c87-ad19-d250cffe1ace" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/StockholdersEquityTables" xlink:type="simple" xlink:href="sncr-20210630.xsd#StockholdersEquityTables"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/StockholdersEquityTables" xlink:type="extended" id="i85d1289828994f3a9031c6fded4b6e42_StockholdersEquityTables">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07e581c1-009d-467b-a8bf-0d1a607b7170" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityTableTextBlock_0ca3c19c-25ab-4410-99a2-598acc52961f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07e581c1-009d-467b-a8bf-0d1a607b7170" xlink:to="loc_us-gaap_TemporaryEquityTableTextBlock_0ca3c19c-25ab-4410-99a2-598acc52961f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCompensationCostForShareBasedPaymentArrangementsAllocationOfShareBasedCompensationCostsByPlanTableTextBlock_6154eaf3-8537-468b-a150-aa1c821ef5d7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfCompensationCostForShareBasedPaymentArrangementsAllocationOfShareBasedCompensationCostsByPlanTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07e581c1-009d-467b-a8bf-0d1a607b7170" xlink:to="loc_us-gaap_ScheduleOfCompensationCostForShareBasedPaymentArrangementsAllocationOfShareBasedCompensationCostsByPlanTableTextBlock_6154eaf3-8537-468b-a150-aa1c821ef5d7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock_3ddf0082-4dde-4223-ae21-a677981aa97f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07e581c1-009d-467b-a8bf-0d1a607b7170" xlink:to="loc_us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock_3ddf0082-4dde-4223-ae21-a677981aa97f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock_f16f7da9-2d06-4c43-8cbd-b0554a81f888" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07e581c1-009d-467b-a8bf-0d1a607b7170" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock_f16f7da9-2d06-4c43-8cbd-b0554a81f888" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonvestedRestrictedStockSharesActivityTableTextBlock_e106564c-c000-40ae-9ff5-9f239057051d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NonvestedRestrictedStockSharesActivityTableTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07e581c1-009d-467b-a8bf-0d1a607b7170" xlink:to="loc_us-gaap_NonvestedRestrictedStockSharesActivityTableTextBlock_e106564c-c000-40ae-9ff5-9f239057051d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_edde2840-33f8-4e11-b03f-ea6e3d6c8433" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_07e581c1-009d-467b-a8bf-0d1a607b7170" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_edde2840-33f8-4e11-b03f-ea6e3d6c8433" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_4a50fbf7-b1b0-45aa-9f2a-2391cd4ff456" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_edde2840-33f8-4e11-b03f-ea6e3d6c8433" xlink:to="loc_us-gaap_AwardTypeAxis_4a50fbf7-b1b0-45aa-9f2a-2391cd4ff456" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_4a50fbf7-b1b0-45aa-9f2a-2391cd4ff456_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_4a50fbf7-b1b0-45aa-9f2a-2391cd4ff456" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_4a50fbf7-b1b0-45aa-9f2a-2391cd4ff456_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fc247d0e-d81d-4be7-b880-dbc6790fa3b5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_4a50fbf7-b1b0-45aa-9f2a-2391cd4ff456" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fc247d0e-d81d-4be7-b880-dbc6790fa3b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_30f6264d-2bab-4df2-8b43-732a50c99f9f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fc247d0e-d81d-4be7-b880-dbc6790fa3b5" xlink:to="loc_us-gaap_RestrictedStockMember_30f6264d-2bab-4df2-8b43-732a50c99f9f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_2b52963a-ba1c-4cf3-a720-6017163db8f5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fc247d0e-d81d-4be7-b880-dbc6790fa3b5" xlink:to="loc_us-gaap_PerformanceSharesMember_2b52963a-ba1c-4cf3-a720-6017163db8f5" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/StockholdersEquityAdditionalInformationDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#StockholdersEquityAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/StockholdersEquityAdditionalInformationDetails" xlink:type="extended" id="i57dcead654454e6da575182801ee3319_StockholdersEquityAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_NumberOfVotesEachShare_2f7b0106-17f0-4d76-b838-8d6509eda3ab" xlink:href="sncr-20210630.xsd#sncr_NumberOfVotesEachShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_sncr_NumberOfVotesEachShare_2f7b0106-17f0-4d76-b838-8d6509eda3ab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Dividends_c3843d1b-d5f4-44fa-807f-778c1272156c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Dividends"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_us-gaap_Dividends_c3843d1b-d5f4-44fa-807f-778c1272156c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_ec4d7d88-99c6-475c-925a-4e92bd239d54" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_ec4d7d88-99c6-475c-925a-4e92bd239d54" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_fe5c856f-1ee8-4055-aa35-fc55626aefc2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_fe5c856f-1ee8-4055-aa35-fc55626aefc2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_f9ba3484-2636-4e6a-ad2a-87d346fe7cd5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_f9ba3484-2636-4e6a-ad2a-87d346fe7cd5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesIssued_c7d77396-e77c-48d3-aa12-943147185e7b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquitySharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_us-gaap_TemporaryEquitySharesIssued_c7d77396-e77c-48d3-aa12-943147185e7b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityParOrStatedValuePerShare_d7a834ae-7721-48a8-a5bc-e412f6d64b41" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_us-gaap_TemporaryEquityParOrStatedValuePerShare_d7a834ae-7721-48a8-a5bc-e412f6d64b41" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityLiquidationPreferencePerShare_373eaa6c-7771-435b-af4f-06ce9f94e047" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityLiquidationPreferencePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_us-gaap_TemporaryEquityLiquidationPreferencePerShare_373eaa6c-7771-435b-af4f-06ce9f94e047" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_PreferredStockDividendRatePercentageOne_30404ab4-59e2-4c10-ab32-e329d8cd0b44" xlink:href="sncr-20210630.xsd#sncr_PreferredStockDividendRatePercentageOne"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_sncr_PreferredStockDividendRatePercentageOne_30404ab4-59e2-4c10-ab32-e329d8cd0b44" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_PreferredStockDividendRatePercentageTwo_0ba7d9be-067c-4366-a71b-73e5b2f757f0" xlink:href="sncr-20210630.xsd#sncr_PreferredStockDividendRatePercentageTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_sncr_PreferredStockDividendRatePercentageTwo_0ba7d9be-067c-4366-a71b-73e5b2f757f0" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_PreferredStockDividendRatePercentageThree_29a18e2e-76c0-49ec-aaf6-0a119d4cc6ca" xlink:href="sncr-20210630.xsd#sncr_PreferredStockDividendRatePercentageThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_sncr_PreferredStockDividendRatePercentageThree_29a18e2e-76c0-49ec-aaf6-0a119d4cc6ca" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityLiquidationValueAndRedemptionValue_2a32b19d-3e73-4fcf-8cdb-4f48e090a9a9" xlink:href="sncr-20210630.xsd#sncr_TemporaryEquityLiquidationValueAndRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_sncr_TemporaryEquityLiquidationValueAndRedemptionValue_2a32b19d-3e73-4fcf-8cdb-4f48e090a9a9" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentProceedsFromSaleOfStockTransactionsUsedForRedemptionOfShares_8749e757-e0ba-4ded-b441-645eac97fba1" xlink:href="sncr-20210630.xsd#sncr_DebtInstrumentProceedsFromSaleOfStockTransactionsUsedForRedemptionOfShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_sncr_DebtInstrumentProceedsFromSaleOfStockTransactionsUsedForRedemptionOfShares_8749e757-e0ba-4ded-b441-645eac97fba1" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_DebtInstrumentProceedsFromSaleOfStockTransactionsUsedForRedemptionOfSharesAndBuyBackOfShares_2b6c56b5-b680-4862-b145-9e535cd91ab1" xlink:href="sncr-20210630.xsd#sncr_DebtInstrumentProceedsFromSaleOfStockTransactionsUsedForRedemptionOfSharesAndBuyBackOfShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_sncr_DebtInstrumentProceedsFromSaleOfStockTransactionsUsedForRedemptionOfSharesAndBuyBackOfShares_2b6c56b5-b680-4862-b145-9e535cd91ab1" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_PreferredStockOwnershipPercentage_84d6b023-0c76-42e3-8c80-701077975da9" xlink:href="sncr-20210630.xsd#sncr_PreferredStockOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_sncr_PreferredStockOwnershipPercentage_84d6b023-0c76-42e3-8c80-701077975da9" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityPreferredStockRedemptionShares_862ce8d8-ab58-4a40-a054-b0157e6106de" xlink:href="sncr-20210630.xsd#sncr_TemporaryEquityPreferredStockRedemptionShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_sncr_TemporaryEquityPreferredStockRedemptionShares_862ce8d8-ab58-4a40-a054-b0157e6106de" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRedeemedOrCalledDuringPeriodShares_e30aec6c-0449-48dc-9698-a3a6b870f04d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockRedeemedOrCalledDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_us-gaap_StockRedeemedOrCalledDuringPeriodShares_e30aec6c-0449-48dc-9698-a3a6b870f04d" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRedeemedOrCalledDuringPeriodValue_2f2cf4c4-df9c-4f8e-88ba-a9dd4b5b43b6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockRedeemedOrCalledDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_us-gaap_StockRedeemedOrCalledDuringPeriodValue_2f2cf4c4-df9c-4f8e-88ba-a9dd4b5b43b6" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityPreferredStockRedemptionValue_ef35de1d-9f00-4bea-96e6-5cf2ea92192f" xlink:href="sncr-20210630.xsd#sncr_TemporaryEquityPreferredStockRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_sncr_TemporaryEquityPreferredStockRedemptionValue_ef35de1d-9f00-4bea-96e6-5cf2ea92192f" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_a19e37bd-6049-4ee5-ab10-1b050593ed76" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_a19e37bd-6049-4ee5-ab10-1b050593ed76" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_7a7e68e7-82b5-4ea1-ba42-163e209be61c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_7a7e68e7-82b5-4ea1-ba42-163e209be61c" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCompensationShareBasedArrangementsLiabilityCurrent_57339020-41e3-4940-9316-23e889d583a0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredCompensationShareBasedArrangementsLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_us-gaap_DeferredCompensationShareBasedArrangementsLiabilityCurrent_57339020-41e3-4940-9316-23e889d583a0" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_09b51a7a-ee03-49df-a91c-f50fd5a0c94f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_09b51a7a-ee03-49df-a91c-f50fd5a0c94f" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f5c084bd-2363-41bf-8a82-aa0575b2f76d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_f258326b-2d0e-4edd-a2bc-73dc4dfb275f" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f5c084bd-2363-41bf-8a82-aa0575b2f76d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_3d972225-15be-463a-86d8-0439a133e4e4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f5c084bd-2363-41bf-8a82-aa0575b2f76d" xlink:to="loc_us-gaap_StatementClassOfStockAxis_3d972225-15be-463a-86d8-0439a133e4e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_3d972225-15be-463a-86d8-0439a133e4e4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_3d972225-15be-463a-86d8-0439a133e4e4" xlink:to="loc_us-gaap_ClassOfStockDomain_3d972225-15be-463a-86d8-0439a133e4e4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_d72ced2e-fc7b-426a-bc65-b5ea76862baf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_3d972225-15be-463a-86d8-0439a133e4e4" xlink:to="loc_us-gaap_ClassOfStockDomain_d72ced2e-fc7b-426a-bc65-b5ea76862baf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_b023b553-cc6f-45a5-9470-c52ec022357d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_d72ced2e-fc7b-426a-bc65-b5ea76862baf" xlink:to="loc_us-gaap_CommonStockMember_b023b553-cc6f-45a5-9470-c52ec022357d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesBPreferredStockMember_6555ddb3-f1d4-4b04-bd9b-8c1337dc6060" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SeriesBPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_d72ced2e-fc7b-426a-bc65-b5ea76862baf" xlink:to="loc_us-gaap_SeriesBPreferredStockMember_6555ddb3-f1d4-4b04-bd9b-8c1337dc6060" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_7d1a306b-1fda-4185-90c5-46091754b2fb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_d72ced2e-fc7b-426a-bc65-b5ea76862baf" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_7d1a306b-1fda-4185-90c5-46091754b2fb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_845dee9a-372f-4015-b4e4-dec8befae53a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f5c084bd-2363-41bf-8a82-aa0575b2f76d" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_845dee9a-372f-4015-b4e4-dec8befae53a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_845dee9a-372f-4015-b4e4-dec8befae53a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_845dee9a-372f-4015-b4e4-dec8befae53a" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_845dee9a-372f-4015-b4e4-dec8befae53a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7b7f26b6-9658-4015-bfba-ab4d7fb4d3bf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_845dee9a-372f-4015-b4e4-dec8befae53a" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7b7f26b6-9658-4015-bfba-ab4d7fb4d3bf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_PublicStockOfferingMember_a3881771-a7b4-442a-aaab-0d23b194caeb" xlink:href="sncr-20210630.xsd#sncr_PublicStockOfferingMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7b7f26b6-9658-4015-bfba-ab4d7fb4d3bf" xlink:to="loc_sncr_PublicStockOfferingMember_a3881771-a7b4-442a-aaab-0d23b194caeb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OverAllotmentOptionMember_a6e53eb0-75c6-4d69-9b1b-6348edf2d424" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OverAllotmentOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7b7f26b6-9658-4015-bfba-ab4d7fb4d3bf" xlink:to="loc_us-gaap_OverAllotmentOptionMember_a6e53eb0-75c6-4d69-9b1b-6348edf2d424" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrivatePlacementMember_2d2dfacc-9a7b-4ac6-af6b-17129ebdbe2e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PrivatePlacementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_7b7f26b6-9658-4015-bfba-ab4d7fb4d3bf" xlink:to="loc_us-gaap_PrivatePlacementMember_2d2dfacc-9a7b-4ac6-af6b-17129ebdbe2e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_4a5b3726-5c83-4027-a42a-5fea2c17a463" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f5c084bd-2363-41bf-8a82-aa0575b2f76d" xlink:to="loc_srt_RangeAxis_4a5b3726-5c83-4027-a42a-5fea2c17a463" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_4a5b3726-5c83-4027-a42a-5fea2c17a463_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_4a5b3726-5c83-4027-a42a-5fea2c17a463" xlink:to="loc_srt_RangeMember_4a5b3726-5c83-4027-a42a-5fea2c17a463_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_c71146cb-838e-48be-8904-5040ab0e4aa4" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_4a5b3726-5c83-4027-a42a-5fea2c17a463" xlink:to="loc_srt_RangeMember_c71146cb-838e-48be-8904-5040ab0e4aa4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_175601b3-cbc6-4d44-85e4-f6a52feb3f52" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c71146cb-838e-48be-8904-5040ab0e4aa4" xlink:to="loc_srt_MinimumMember_175601b3-cbc6-4d44-85e4-f6a52feb3f52" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_4b775fbe-b488-4496-8320-d34574e511cd" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c71146cb-838e-48be-8904-5040ab0e4aa4" xlink:to="loc_srt_MaximumMember_4b775fbe-b488-4496-8320-d34574e511cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_1753543f-cc2b-4b84-99f2-2265f77b0e90" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f5c084bd-2363-41bf-8a82-aa0575b2f76d" xlink:to="loc_srt_CounterpartyNameAxis_1753543f-cc2b-4b84-99f2-2265f77b0e90" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_1753543f-cc2b-4b84-99f2-2265f77b0e90_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_1753543f-cc2b-4b84-99f2-2265f77b0e90" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_1753543f-cc2b-4b84-99f2-2265f77b0e90_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_12a12792-0b3e-49bc-ad5f-a2ef4fc7898d" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_1753543f-cc2b-4b84-99f2-2265f77b0e90" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_12a12792-0b3e-49bc-ad5f-a2ef4fc7898d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_SilverPrivateHoldingsILLCMember_2335cb72-67f6-4c6c-986a-644abba0ba65" xlink:href="sncr-20210630.xsd#sncr_SilverPrivateHoldingsILLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_12a12792-0b3e-49bc-ad5f-a2ef4fc7898d" xlink:to="loc_sncr_SilverPrivateHoldingsILLCMember_2335cb72-67f6-4c6c-986a-644abba0ba65" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_62d7e84c-e664-4865-8a7a-b08337c1cce2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_f5c084bd-2363-41bf-8a82-aa0575b2f76d" xlink:to="loc_us-gaap_PlanNameAxis_62d7e84c-e664-4865-8a7a-b08337c1cce2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_62d7e84c-e664-4865-8a7a-b08337c1cce2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_62d7e84c-e664-4865-8a7a-b08337c1cce2" xlink:to="loc_us-gaap_PlanNameDomain_62d7e84c-e664-4865-8a7a-b08337c1cce2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_e0005e49-752d-4d4e-a149-7fb6e674e450" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_62d7e84c-e664-4865-8a7a-b08337c1cce2" xlink:to="loc_us-gaap_PlanNameDomain_e0005e49-752d-4d4e-a149-7fb6e674e450" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_EquityIncentivePlan2015Member_606f9fd4-a725-4444-a30d-fd611940615a" xlink:href="sncr-20210630.xsd#sncr_EquityIncentivePlan2015Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_e0005e49-752d-4d4e-a149-7fb6e674e450" xlink:to="loc_sncr_EquityIncentivePlan2015Member_606f9fd4-a725-4444-a30d-fd611940615a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_NewHireEquityIncentivePlan2017Member_ca1a49c7-60af-414f-b61b-7b94e1f72f69" xlink:href="sncr-20210630.xsd#sncr_NewHireEquityIncentivePlan2017Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_e0005e49-752d-4d4e-a149-7fb6e674e450" xlink:to="loc_sncr_NewHireEquityIncentivePlan2017Member_ca1a49c7-60af-414f-b61b-7b94e1f72f69" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/StockholdersEquityPreferredStockDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#StockholdersEquityPreferredStockDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/StockholdersEquityPreferredStockDetails" xlink:type="extended" id="i740006e62fff4ea9bcdb1224144bc2fc_StockholdersEquityPreferredStockDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityLineItems_4a739904-4976-4102-8028-70be19f3cb16" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_2886a516-c9da-4845-b62d-19d602642ecd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInTemporaryEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TemporaryEquityLineItems_4a739904-4976-4102-8028-70be19f3cb16" xlink:to="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_2886a516-c9da-4845-b62d-19d602642ecd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_78ef7fe5-4cf2-48d1-a466-fd7deb162f9b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_2886a516-c9da-4845-b62d-19d602642ecd" xlink:to="loc_us-gaap_TemporaryEquitySharesOutstanding_78ef7fe5-4cf2-48d1-a466-fd7deb162f9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityStockIssuedDuringPeriodSharesNewIssues_c8f8117e-9fd2-4f4a-befb-aae9ffaf0ad2" xlink:href="sncr-20210630.xsd#sncr_TemporaryEquityStockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_2886a516-c9da-4845-b62d-19d602642ecd" xlink:to="loc_sncr_TemporaryEquityStockIssuedDuringPeriodSharesNewIssues_c8f8117e-9fd2-4f4a-befb-aae9ffaf0ad2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityAmortizationShares_16f73b25-b31a-4ca5-bcf9-77fe80712de6" xlink:href="sncr-20210630.xsd#sncr_TemporaryEquityAmortizationShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_2886a516-c9da-4845-b62d-19d602642ecd" xlink:to="loc_sncr_TemporaryEquityAmortizationShares_16f73b25-b31a-4ca5-bcf9-77fe80712de6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityDividendsShares_836c526e-11f9-437a-83e3-53352a226071" xlink:href="sncr-20210630.xsd#sncr_TemporaryEquityDividendsShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_2886a516-c9da-4845-b62d-19d602642ecd" xlink:to="loc_sncr_TemporaryEquityDividendsShares_836c526e-11f9-437a-83e3-53352a226071" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityPaymentOfPreferredDividendShares_e8a623fc-1a23-4de7-9d5b-33b1a1094b6d" xlink:href="sncr-20210630.xsd#sncr_TemporaryEquityPaymentOfPreferredDividendShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_2886a516-c9da-4845-b62d-19d602642ecd" xlink:to="loc_sncr_TemporaryEquityPaymentOfPreferredDividendShares_e8a623fc-1a23-4de7-9d5b-33b1a1094b6d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityPreferredStockRedemptionShares_b9b37c9e-b0d0-4dc2-91d5-cc3b92470ed3" xlink:href="sncr-20210630.xsd#sncr_TemporaryEquityPreferredStockRedemptionShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_2886a516-c9da-4845-b62d-19d602642ecd" xlink:to="loc_sncr_TemporaryEquityPreferredStockRedemptionShares_b9b37c9e-b0d0-4dc2-91d5-cc3b92470ed3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquitySharesOutstanding_aef001e1-7b0d-4ae2-b30f-bcdeddfa854f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquitySharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests_d8bd6d78-2149-45e9-9968-57da95f338c9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_2886a516-c9da-4845-b62d-19d602642ecd" xlink:to="loc_us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests_d8bd6d78-2149-45e9-9968-57da95f338c9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues_d03007b7-6755-4193-99e0-2dffa28a0ab9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_2886a516-c9da-4845-b62d-19d602642ecd" xlink:to="loc_us-gaap_TemporaryEquityStockIssuedDuringPeriodValueNewIssues_d03007b7-6755-4193-99e0-2dffa28a0ab9" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityAmortization_ce0db04f-099c-4a5c-8c5b-5d655ce264c1" xlink:href="sncr-20210630.xsd#sncr_TemporaryEquityAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_2886a516-c9da-4845-b62d-19d602642ecd" xlink:to="loc_sncr_TemporaryEquityAmortization_ce0db04f-099c-4a5c-8c5b-5d655ce264c1" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityDividendsValue_8f19896f-67fa-4c1d-b3ba-c87dd4cee70d" xlink:href="sncr-20210630.xsd#sncr_TemporaryEquityDividendsValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_2886a516-c9da-4845-b62d-19d602642ecd" xlink:to="loc_sncr_TemporaryEquityDividendsValue_8f19896f-67fa-4c1d-b3ba-c87dd4cee70d" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityPaymentOfPreferredDividend_485d72eb-09dd-4fa6-8895-b7b76535b024" xlink:href="sncr-20210630.xsd#sncr_TemporaryEquityPaymentOfPreferredDividend"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_2886a516-c9da-4845-b62d-19d602642ecd" xlink:to="loc_sncr_TemporaryEquityPaymentOfPreferredDividend_485d72eb-09dd-4fa6-8895-b7b76535b024" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TemporaryEquityPreferredStockRedemptionValue_f18a484d-4c7c-4b04-9683-bc8487d2413f" xlink:href="sncr-20210630.xsd#sncr_TemporaryEquityPreferredStockRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInTemporaryEquityRollForward_2886a516-c9da-4845-b62d-19d602642ecd" xlink:to="loc_sncr_TemporaryEquityPreferredStockRedemptionValue_f18a484d-4c7c-4b04-9683-bc8487d2413f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests_4200ce66-adb5-43cf-9e4d-a7ada09cdf5d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TemporaryEquityCarryingAmountIncludingPortionAttributableToNoncontrollingInterests"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_45e6d998-d95f-4949-a200-a0107f3a7aa2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_TemporaryEquityLineItems_4a739904-4976-4102-8028-70be19f3cb16" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_45e6d998-d95f-4949-a200-a0107f3a7aa2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_9c060cab-b792-4ced-9911-3c025eab0145" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_45e6d998-d95f-4949-a200-a0107f3a7aa2" xlink:to="loc_us-gaap_StatementClassOfStockAxis_9c060cab-b792-4ced-9911-3c025eab0145" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_9c060cab-b792-4ced-9911-3c025eab0145_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_9c060cab-b792-4ced-9911-3c025eab0145" xlink:to="loc_us-gaap_ClassOfStockDomain_9c060cab-b792-4ced-9911-3c025eab0145_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_0baf481a-3b1b-4a13-b562-def475355a04" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_9c060cab-b792-4ced-9911-3c025eab0145" xlink:to="loc_us-gaap_ClassOfStockDomain_0baf481a-3b1b-4a13-b562-def475355a04" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesBPreferredStockMember_2dc55053-8179-4107-80a8-8fea91dd7cd6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SeriesBPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_0baf481a-3b1b-4a13-b562-def475355a04" xlink:to="loc_us-gaap_SeriesBPreferredStockMember_2dc55053-8179-4107-80a8-8fea91dd7cd6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_3c108477-e528-4c19-803e-3c6d9858e035" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_0baf481a-3b1b-4a13-b562-def475355a04" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_3c108477-e528-4c19-803e-3c6d9858e035" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/StockholdersEquityStockbasedCompensationDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#StockholdersEquityStockbasedCompensationDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/StockholdersEquityStockbasedCompensationDetails" xlink:type="extended" id="id996bb1697fb4f47944107786b478bce_StockholdersEquityStockbasedCompensationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_51149fb6-36b3-4754-b376-2cbddf6885b3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAggregateDisclosuresAbstract_bd876d76-095d-484f-8083-f588af046169" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationAggregateDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_51149fb6-36b3-4754-b376-2cbddf6885b3" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationAggregateDisclosuresAbstract_bd876d76-095d-484f-8083-f588af046169" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_48cf80ef-4e97-4760-90d4-632d7ccb2eb9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAggregateDisclosuresAbstract_bd876d76-095d-484f-8083-f588af046169" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_48cf80ef-4e97-4760-90d4-632d7ccb2eb9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_ac37cc60-f8a0-47fb-b33c-8e7b60a7045b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAggregateDisclosuresAbstract_bd876d76-095d-484f-8083-f588af046169" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_ac37cc60-f8a0-47fb-b33c-8e7b60a7045b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_93400464-1b38-48c2-bddb-b143a3588e98" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAggregateDisclosuresAbstract_bd876d76-095d-484f-8083-f588af046169" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_93400464-1b38-48c2-bddb-b143a3588e98" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_339eeed5-3f95-455f-97a0-c82ed0e7129f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAggregateDisclosuresAbstract_bd876d76-095d-484f-8083-f588af046169" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_339eeed5-3f95-455f-97a0-c82ed0e7129f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_5c11021d-38c0-4a55-8eff-f3bf74ab76c1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_51149fb6-36b3-4754-b376-2cbddf6885b3" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_5c11021d-38c0-4a55-8eff-f3bf74ab76c1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_63afc78c-04a4-46a8-897f-cdfcc06c3876" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_5c11021d-38c0-4a55-8eff-f3bf74ab76c1" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_63afc78c-04a4-46a8-897f-cdfcc06c3876" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_63afc78c-04a4-46a8-897f-cdfcc06c3876_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_63afc78c-04a4-46a8-897f-cdfcc06c3876" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_63afc78c-04a4-46a8-897f-cdfcc06c3876_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_3497fb2d-5eb2-4241-a66e-6f2cbcffbb40" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_63afc78c-04a4-46a8-897f-cdfcc06c3876" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_3497fb2d-5eb2-4241-a66e-6f2cbcffbb40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_91bb2c17-9877-43af-a829-07d6decec01f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_3497fb2d-5eb2-4241-a66e-6f2cbcffbb40" xlink:to="loc_us-gaap_CostOfSalesMember_91bb2c17-9877-43af-a829-07d6decec01f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_424e7597-074a-4562-9143-89dd3e0fdb32" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_3497fb2d-5eb2-4241-a66e-6f2cbcffbb40" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_424e7597-074a-4562-9143-89dd3e0fdb32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_479f7b07-ea54-427d-bc40-237d73e4ca4d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_3497fb2d-5eb2-4241-a66e-6f2cbcffbb40" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_479f7b07-ea54-427d-bc40-237d73e4ca4d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_b3899bb7-c44e-4c41-b000-e16f2907f018" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_5c11021d-38c0-4a55-8eff-f3bf74ab76c1" xlink:to="loc_us-gaap_AwardTypeAxis_b3899bb7-c44e-4c41-b000-e16f2907f018" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b3899bb7-c44e-4c41-b000-e16f2907f018_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_b3899bb7-c44e-4c41-b000-e16f2907f018" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b3899bb7-c44e-4c41-b000-e16f2907f018_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_69255ea8-dd8d-4b5a-9fe6-56001fe31684" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_b3899bb7-c44e-4c41-b000-e16f2907f018" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_69255ea8-dd8d-4b5a-9fe6-56001fe31684" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_EmployeeAndDirectorsStockOptionsMember_4996a79b-bcad-48b6-8fc2-7ec492224966" xlink:href="sncr-20210630.xsd#sncr_EmployeeAndDirectorsStockOptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_69255ea8-dd8d-4b5a-9fe6-56001fe31684" xlink:to="loc_sncr_EmployeeAndDirectorsStockOptionsMember_4996a79b-bcad-48b6-8fc2-7ec492224966" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_f640cd4f-beec-4332-8bc1-963ca4df0d0e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_69255ea8-dd8d-4b5a-9fe6-56001fe31684" xlink:to="loc_us-gaap_RestrictedStockMember_f640cd4f-beec-4332-8bc1-963ca4df0d0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_4d351f68-59d5-449a-9a57-c5c8297d7139" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_69255ea8-dd8d-4b5a-9fe6-56001fe31684" xlink:to="loc_us-gaap_PerformanceSharesMember_4d351f68-59d5-449a-9a57-c5c8297d7139" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/StockholdersEquityBlackScholesAssumptionsDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#StockholdersEquityBlackScholesAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/StockholdersEquityBlackScholesAssumptionsDetails" xlink:type="extended" id="i4517a8e6551047158b816a200a9679f8_StockholdersEquityBlackScholesAssumptionsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0ac31eb4-0534-48ce-b0ac-5dcf5829da30" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_8c4c11cf-baa7-4c0d-801f-bae82418f521" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0ac31eb4-0534-48ce-b0ac-5dcf5829da30" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_8c4c11cf-baa7-4c0d-801f-bae82418f521" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_acd995f0-fdb7-49c6-8318-0b4a7e69be9b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_8c4c11cf-baa7-4c0d-801f-bae82418f521" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_acd995f0-fdb7-49c6-8318-0b4a7e69be9b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_a2753359-6c52-4b9d-9e20-13f34364e12d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_8c4c11cf-baa7-4c0d-801f-bae82418f521" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_a2753359-6c52-4b9d-9e20-13f34364e12d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_21472690-6b3b-433d-bd93-84ce39cc90b9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_8c4c11cf-baa7-4c0d-801f-bae82418f521" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_21472690-6b3b-433d-bd93-84ce39cc90b9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_9d714142-37d8-4a0c-9533-a453632adaeb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_8c4c11cf-baa7-4c0d-801f-bae82418f521" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_9d714142-37d8-4a0c-9533-a453632adaeb" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_54d55330-c509-4236-abfd-a7231af52905" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsAndMethodologyAbstract_8c4c11cf-baa7-4c0d-801f-bae82418f521" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_54d55330-c509-4236-abfd-a7231af52905" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_15d17bee-6b11-4528-ba43-644ac1c6a65d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_0ac31eb4-0534-48ce-b0ac-5dcf5829da30" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_15d17bee-6b11-4528-ba43-644ac1c6a65d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_c822cd1a-b8bb-42d2-bafb-b32a8f3879cb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_15d17bee-6b11-4528-ba43-644ac1c6a65d" xlink:to="loc_us-gaap_AwardTypeAxis_c822cd1a-b8bb-42d2-bafb-b32a8f3879cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c822cd1a-b8bb-42d2-bafb-b32a8f3879cb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_c822cd1a-b8bb-42d2-bafb-b32a8f3879cb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c822cd1a-b8bb-42d2-bafb-b32a8f3879cb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1a2005fa-1d8b-4a71-b8ef-880a8e27608b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_c822cd1a-b8bb-42d2-bafb-b32a8f3879cb" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1a2005fa-1d8b-4a71-b8ef-880a8e27608b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_EmployeeAndDirectorsStockOptionsMember_76a543d6-0189-485b-8f06-f45129ad189c" xlink:href="sncr-20210630.xsd#sncr_EmployeeAndDirectorsStockOptionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_1a2005fa-1d8b-4a71-b8ef-880a8e27608b" xlink:to="loc_sncr_EmployeeAndDirectorsStockOptionsMember_76a543d6-0189-485b-8f06-f45129ad189c" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/StockholdersEquityRestrictedStockandPerformanceStockDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#StockholdersEquityRestrictedStockandPerformanceStockDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/StockholdersEquityRestrictedStockandPerformanceStockDetails" xlink:type="extended" id="i881eeecb21c3412a929f6f3a6ae6786a_StockholdersEquityRestrictedStockandPerformanceStockDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f345836f-a48f-43fa-b55f-3f4a483c6505" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_06ba12d4-2838-46f4-bedb-53e0fd8d1369" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f345836f-a48f-43fa-b55f-3f4a483c6505" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_06ba12d4-2838-46f4-bedb-53e0fd8d1369" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_b9960841-e263-43a5-b5ed-60799dba88e3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_06ba12d4-2838-46f4-bedb-53e0fd8d1369" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_b9960841-e263-43a5-b5ed-60799dba88e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_c6b99cbf-9d1d-4695-b830-1953c95a435b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_06ba12d4-2838-46f4-bedb-53e0fd8d1369" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_c6b99cbf-9d1d-4695-b830-1953c95a435b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsAdjustmentInPeriod_d97dedb6-21c2-4472-942d-52bafa32fc7b" xlink:href="sncr-20210630.xsd#sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsAdjustmentInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_06ba12d4-2838-46f4-bedb-53e0fd8d1369" xlink:to="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsAdjustmentInPeriod_d97dedb6-21c2-4472-942d-52bafa32fc7b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_79b3a3eb-c751-4748-b041-bb39670acff3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_06ba12d4-2838-46f4-bedb-53e0fd8d1369" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_79b3a3eb-c751-4748-b041-bb39670acff3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_9178dbd0-cbc7-4c3f-9282-7318df38be75" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_06ba12d4-2838-46f4-bedb-53e0fd8d1369" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_9178dbd0-cbc7-4c3f-9282-7318df38be75" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_cda9c81b-0999-4cdc-a27c-79afa7f6796d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_d8657fe4-b77d-4a6d-9ce2-824d86176546" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f345836f-a48f-43fa-b55f-3f4a483c6505" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_d8657fe4-b77d-4a6d-9ce2-824d86176546" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_3ea99cc7-84aa-4f0d-a195-f6a817c9235a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_d8657fe4-b77d-4a6d-9ce2-824d86176546" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_3ea99cc7-84aa-4f0d-a195-f6a817c9235a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_2de7d8fc-89c9-4ec3-83e7-69120c673911" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_d8657fe4-b77d-4a6d-9ce2-824d86176546" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_2de7d8fc-89c9-4ec3-83e7-69120c673911" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsAdjustmentInPeriodWeightedAverageGrantDateFairValue_c415e730-dd58-4b0a-beeb-fd75ca6afa44" xlink:href="sncr-20210630.xsd#sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsAdjustmentInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_d8657fe4-b77d-4a6d-9ce2-824d86176546" xlink:to="loc_sncr_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsAdjustmentInPeriodWeightedAverageGrantDateFairValue_c415e730-dd58-4b0a-beeb-fd75ca6afa44" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_60038dc1-eca6-4658-95eb-92092143b2ce" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_d8657fe4-b77d-4a6d-9ce2-824d86176546" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_60038dc1-eca6-4658-95eb-92092143b2ce" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_b022ec51-fefa-460c-b5d4-a3b130983a40" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsAdditionalDisclosuresAbstract_d8657fe4-b77d-4a6d-9ce2-824d86176546" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_b022ec51-fefa-460c-b5d4-a3b130983a40" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_15e27db0-6357-4c45-8487-5b670e353335" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_2b4241cf-e145-4f23-83b6-22d5236ee8ab" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f345836f-a48f-43fa-b55f-3f4a483c6505" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_2b4241cf-e145-4f23-83b6-22d5236ee8ab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_93f93116-e708-4e0a-b332-b503fdca312b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_f345836f-a48f-43fa-b55f-3f4a483c6505" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_93f93116-e708-4e0a-b332-b503fdca312b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_fabafcad-2e2e-43ef-be17-fd396ced68d8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_93f93116-e708-4e0a-b332-b503fdca312b" xlink:to="loc_us-gaap_AwardTypeAxis_fabafcad-2e2e-43ef-be17-fd396ced68d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fabafcad-2e2e-43ef-be17-fd396ced68d8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_fabafcad-2e2e-43ef-be17-fd396ced68d8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_fabafcad-2e2e-43ef-be17-fd396ced68d8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a21e6f48-34b7-400b-86d2-8708b2f198ac" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_fabafcad-2e2e-43ef-be17-fd396ced68d8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a21e6f48-34b7-400b-86d2-8708b2f198ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_cf1056da-30b4-46e2-ad9c-b395790befb4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a21e6f48-34b7-400b-86d2-8708b2f198ac" xlink:to="loc_us-gaap_RestrictedStockMember_cf1056da-30b4-46e2-ad9c-b395790befb4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_5fccbacf-4ffb-4b43-b7c5-50158095e60d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a21e6f48-34b7-400b-86d2-8708b2f198ac" xlink:to="loc_us-gaap_PerformanceSharesMember_5fccbacf-4ffb-4b43-b7c5-50158095e60d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_da30babb-aadb-4afb-920e-fbb3a987d69a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_93f93116-e708-4e0a-b332-b503fdca312b" xlink:to="loc_us-gaap_PlanNameAxis_da30babb-aadb-4afb-920e-fbb3a987d69a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_da30babb-aadb-4afb-920e-fbb3a987d69a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_da30babb-aadb-4afb-920e-fbb3a987d69a" xlink:to="loc_us-gaap_PlanNameDomain_da30babb-aadb-4afb-920e-fbb3a987d69a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_3b030e89-1579-4d88-82c2-a17ca7008757" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_da30babb-aadb-4afb-920e-fbb3a987d69a" xlink:to="loc_us-gaap_PlanNameDomain_3b030e89-1579-4d88-82c2-a17ca7008757" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_EquityIncentivePlan2015Member_132f4f1c-105d-4865-b059-179384e22f36" xlink:href="sncr-20210630.xsd#sncr_EquityIncentivePlan2015Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_3b030e89-1579-4d88-82c2-a17ca7008757" xlink:to="loc_sncr_EquityIncentivePlan2015Member_132f4f1c-105d-4865-b059-179384e22f36" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/RestructuringDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#RestructuringDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/RestructuringDetails" xlink:type="extended" id="ie61eb189b77f4b9183ac6ec4ee11d019_RestructuringDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_ab956871-aac6-4336-9129-d3cbfa25034e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_65fc8969-191e-4335-9f97-c0ab2378023d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_ab956871-aac6-4336-9129-d3cbfa25034e" xlink:to="loc_us-gaap_RestructuringReserve_65fc8969-191e-4335-9f97-c0ab2378023d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_2d4c627b-9b10-47a3-aa7a-0d623bbb170e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_ab956871-aac6-4336-9129-d3cbfa25034e" xlink:to="loc_us-gaap_RestructuringCharges_2d4c627b-9b10-47a3-aa7a-0d623bbb170e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRestructuring_37b39a2d-a922-41a8-bbfe-57ad089e0834" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsForRestructuring"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_ab956871-aac6-4336-9129-d3cbfa25034e" xlink:to="loc_us-gaap_PaymentsForRestructuring_37b39a2d-a922-41a8-bbfe-57ad089e0834" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveTranslationAndOtherAdjustment_f69244ab-cccc-4598-9649-83bd96635500" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringReserveTranslationAndOtherAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_ab956871-aac6-4336-9129-d3cbfa25034e" xlink:to="loc_us-gaap_RestructuringReserveTranslationAndOtherAdjustment_f69244ab-cccc-4598-9649-83bd96635500" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_e5486db1-648a-48b5-ae4f-ff9167870343" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringReserve"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_5144eaf9-a1bb-4929-86fd-b90bc58840ed" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_ab956871-aac6-4336-9129-d3cbfa25034e" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_5144eaf9-a1bb-4929-86fd-b90bc58840ed" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_f179d946-58f4-4505-abbf-a7a2d01b57dd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_5144eaf9-a1bb-4929-86fd-b90bc58840ed" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_f179d946-58f4-4505-abbf-a7a2d01b57dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_f179d946-58f4-4505-abbf-a7a2d01b57dd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_f179d946-58f4-4505-abbf-a7a2d01b57dd" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_f179d946-58f4-4505-abbf-a7a2d01b57dd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_96b7f0f7-47d5-42a4-bc01-212b4ce9d7e2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_f179d946-58f4-4505-abbf-a7a2d01b57dd" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_96b7f0f7-47d5-42a4-bc01-212b4ce9d7e2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_7a59fc32-fbfd-4927-bc5c-a58a2c6cc815" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_96b7f0f7-47d5-42a4-bc01-212b4ce9d7e2" xlink:to="loc_us-gaap_EmployeeSeveranceMember_7a59fc32-fbfd-4927-bc5c-a58a2c6cc815" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/EarningsperCommonShareEPSDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#EarningsperCommonShareEPSDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/EarningsperCommonShareEPSDetails" xlink:type="extended" id="iffcb6338b1764161a418319bca99bac8_EarningsperCommonShareEPSDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasicLineItems_0ae83fe7-71af-4d60-ba4e-e247a4493b32" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareBasicLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareReconciliationAbstract_316afd5b-2ed5-43ed-9e57-db8d453148bb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareReconciliationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_0ae83fe7-71af-4d60-ba4e-e247a4493b32" xlink:to="loc_us-gaap_EarningsPerShareReconciliationAbstract_316afd5b-2ed5-43ed-9e57-db8d453148bb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest_46845c8f-a40e-4fbc-ac5f-f8a25f437ea4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareReconciliationAbstract_316afd5b-2ed5-43ed-9e57-db8d453148bb" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest_46845c8f-a40e-4fbc-ac5f-f8a25f437ea4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_8d13a7b4-46d5-4190-9156-f788bc65c0cc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareReconciliationAbstract_316afd5b-2ed5-43ed-9e57-db8d453148bb" xlink:to="loc_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_8d13a7b4-46d5-4190-9156-f788bc65c0cc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockDividendsAndOtherAdjustments_6920d09f-fc3b-4db0-a322-680758ba5612" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PreferredStockDividendsAndOtherAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareReconciliationAbstract_316afd5b-2ed5-43ed-9e57-db8d453148bb" xlink:to="loc_us-gaap_PreferredStockDividendsAndOtherAdjustments_6920d09f-fc3b-4db0-a322-680758ba5612" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_c1da13fc-fc2d-4ee4-b83e-e1979f8a79f7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareReconciliationAbstract_316afd5b-2ed5-43ed-9e57-db8d453148bb" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_c1da13fc-fc2d-4ee4-b83e-e1979f8a79f7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperations_59995033-46a3-4bc8-8c54-0e6988113cd0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeLossFromContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareReconciliationAbstract_316afd5b-2ed5-43ed-9e57-db8d453148bb" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperations_59995033-46a3-4bc8-8c54-0e6988113cd0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_bda007dd-d4b0-41fa-bc14-e2dcfc69d2ca" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareReconciliationAbstract_316afd5b-2ed5-43ed-9e57-db8d453148bb" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_bda007dd-d4b0-41fa-bc14-e2dcfc69d2ca" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_a4a2a294-b1a6-468d-a3cd-f88e76958e5e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_bda007dd-d4b0-41fa-bc14-e2dcfc69d2ca" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_a4a2a294-b1a6-468d-a3cd-f88e76958e5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_571f8f97-1b31-49dc-8f75-ccde67b4dc5c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_bda007dd-d4b0-41fa-bc14-e2dcfc69d2ca" xlink:to="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_571f8f97-1b31-49dc-8f75-ccde67b4dc5c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToConversionOfPreferredStock_f0af5a5b-f8ae-41e4-b8f7-4139481f3bec" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncrementalCommonSharesAttributableToConversionOfPreferredStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_571f8f97-1b31-49dc-8f75-ccde67b4dc5c" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToConversionOfPreferredStock_f0af5a5b-f8ae-41e4-b8f7-4139481f3bec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_f5b424c1-4567-433c-967e-e9551b2e8289" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_571f8f97-1b31-49dc-8f75-ccde67b4dc5c" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_f5b424c1-4567-433c-967e-e9551b2e8289" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_80b51e5e-4258-4344-bbf6-2cf741aa2147" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_571f8f97-1b31-49dc-8f75-ccde67b4dc5c" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_80b51e5e-4258-4344-bbf6-2cf741aa2147" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_6a0adc13-ec7e-4224-9d04-649db8cb7730" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareBasicAndDilutedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareReconciliationAbstract_316afd5b-2ed5-43ed-9e57-db8d453148bb" xlink:to="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_6a0adc13-ec7e-4224-9d04-649db8cb7730" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_e3a9b834-4889-4270-a34f-4d20fcd4deba" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_6a0adc13-ec7e-4224-9d04-649db8cb7730" xlink:to="loc_us-gaap_EarningsPerShareBasic_e3a9b834-4889-4270-a34f-4d20fcd4deba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_b6ab34cc-5e14-427c-9574-1926eb37a143" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_6a0adc13-ec7e-4224-9d04-649db8cb7730" xlink:to="loc_us-gaap_EarningsPerShareDiluted_b6ab34cc-5e14-427c-9574-1926eb37a143" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_321621a0-0cff-416e-ad5a-9b68cb36f6b1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_0ae83fe7-71af-4d60-ba4e-e247a4493b32" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_321621a0-0cff-416e-ad5a-9b68cb36f6b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_PreferredStockConversionRatio_698e670f-3dbc-4ea9-81c9-b837091e1c00" xlink:href="sncr-20210630.xsd#sncr_PreferredStockConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_0ae83fe7-71af-4d60-ba4e-e247a4493b32" xlink:to="loc_sncr_PreferredStockConversionRatio_698e670f-3dbc-4ea9-81c9-b837091e1c00" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_ShareBasedCompensationArrangementsByShareBasedPaymentAwardEquityInstrumentOtherThanOptionsConversionRatio_17e9e94e-fe0e-4e56-aba8-bac2b47458bf" xlink:href="sncr-20210630.xsd#sncr_ShareBasedCompensationArrangementsByShareBasedPaymentAwardEquityInstrumentOtherThanOptionsConversionRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_0ae83fe7-71af-4d60-ba4e-e247a4493b32" xlink:to="loc_sncr_ShareBasedCompensationArrangementsByShareBasedPaymentAwardEquityInstrumentOtherThanOptionsConversionRatio_17e9e94e-fe0e-4e56-aba8-bac2b47458bf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_a876b9f0-f708-451d-9010-fc94ecd13868" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_0ae83fe7-71af-4d60-ba4e-e247a4493b32" xlink:to="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_a876b9f0-f708-451d-9010-fc94ecd13868" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_e15b7bcd-66fe-4427-a5f9-6efa54f3a27f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_a876b9f0-f708-451d-9010-fc94ecd13868" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_e15b7bcd-66fe-4427-a5f9-6efa54f3a27f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_e15b7bcd-66fe-4427-a5f9-6efa54f3a27f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_e15b7bcd-66fe-4427-a5f9-6efa54f3a27f" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_e15b7bcd-66fe-4427-a5f9-6efa54f3a27f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_3d65130f-3a4b-41ad-974a-7f7468d12d80" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_e15b7bcd-66fe-4427-a5f9-6efa54f3a27f" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_3d65130f-3a4b-41ad-974a-7f7468d12d80" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_c900d532-04f7-4aad-86b1-b9cfd29c2aa6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_3d65130f-3a4b-41ad-974a-7f7468d12d80" xlink:to="loc_us-gaap_EmployeeStockOptionMember_c900d532-04f7-4aad-86b1-b9cfd29c2aa6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_7b3f9044-a6b4-423d-95d4-760548152dc2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_3d65130f-3a4b-41ad-974a-7f7468d12d80" xlink:to="loc_us-gaap_RestrictedStockMember_7b3f9044-a6b4-423d-95d4-760548152dc2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_75922648-2ca1-45b2-89db-331e31943016" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_3d65130f-3a4b-41ad-974a-7f7468d12d80" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_75922648-2ca1-45b2-89db-331e31943016" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_23332ab8-276c-4417-94de-45816a8765c4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_3d65130f-3a4b-41ad-974a-7f7468d12d80" xlink:to="loc_us-gaap_PerformanceSharesMember_23332ab8-276c-4417-94de-45816a8765c4" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://synchronoss.com/role/CommitmentandContingenciesAdditionalInformationDetails" xlink:type="simple" xlink:href="sncr-20210630.xsd#CommitmentandContingenciesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://synchronoss.com/role/CommitmentandContingenciesAdditionalInformationDetails" xlink:type="extended" id="i65b4e2eed5294a3faa74e9a6a486e720_CommitmentandContingenciesAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_96ca5c6e-a0e1-4c0b-8c66-1f5d69e5f043" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNewClaimsFiledNumber_92301c1f-0b2d-40fe-b2ea-cb454d032c78" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LossContingencyNewClaimsFiledNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_96ca5c6e-a0e1-4c0b-8c66-1f5d69e5f043" xlink:to="loc_us-gaap_LossContingencyNewClaimsFiledNumber_92301c1f-0b2d-40fe-b2ea-cb454d032c78" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_3e1cec2f-6248-48f0-8bb7-4b5942446994" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_96ca5c6e-a0e1-4c0b-8c66-1f5d69e5f043" xlink:to="loc_us-gaap_LossContingenciesTable_3e1cec2f-6248-48f0-8bb7-4b5942446994" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseAxis_decab49e-acb3-4e17-9189-4cdd6f652e34" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_LitigationCaseAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_3e1cec2f-6248-48f0-8bb7-4b5942446994" xlink:to="loc_srt_LitigationCaseAxis_decab49e-acb3-4e17-9189-4cdd6f652e34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_decab49e-acb3-4e17-9189-4cdd6f652e34_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_LitigationCaseAxis_decab49e-acb3-4e17-9189-4cdd6f652e34" xlink:to="loc_srt_LitigationCaseTypeDomain_decab49e-acb3-4e17-9189-4cdd6f652e34_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_99134d34-50cc-44c1-bf59-0267d0284de6" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_LitigationCaseAxis_decab49e-acb3-4e17-9189-4cdd6f652e34" xlink:to="loc_srt_LitigationCaseTypeDomain_99134d34-50cc-44c1-bf59-0267d0284de6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sncr_TheSecuritiesLawActionsMember_89ae1fda-a9fc-49c1-8cce-780f074f1942" xlink:href="sncr-20210630.xsd#sncr_TheSecuritiesLawActionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_LitigationCaseTypeDomain_99134d34-50cc-44c1-bf59-0267d0284de6" xlink:to="loc_sncr_TheSecuritiesLawActionsMember_89ae1fda-a9fc-49c1-8cce-780f074f1942" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationStatusAxis_f8ea5cbf-9fd4-47de-af4b-12b7f9053ef7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LitigationStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_3e1cec2f-6248-48f0-8bb7-4b5942446994" xlink:to="loc_us-gaap_LitigationStatusAxis_f8ea5cbf-9fd4-47de-af4b-12b7f9053ef7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationStatusDomain_f8ea5cbf-9fd4-47de-af4b-12b7f9053ef7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LitigationStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LitigationStatusAxis_f8ea5cbf-9fd4-47de-af4b-12b7f9053ef7" xlink:to="loc_us-gaap_LitigationStatusDomain_f8ea5cbf-9fd4-47de-af4b-12b7f9053ef7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationStatusDomain_b7872895-9d3e-4e7e-8fb7-583c021e7300" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LitigationStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LitigationStatusAxis_f8ea5cbf-9fd4-47de-af4b-12b7f9053ef7" xlink:to="loc_us-gaap_LitigationStatusDomain_b7872895-9d3e-4e7e-8fb7-583c021e7300" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PendingLitigationMember_5b26eb4d-debc-4a70-9138-cb7cebd4657b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PendingLitigationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LitigationStatusDomain_b7872895-9d3e-4e7e-8fb7-583c021e7300" xlink:to="loc_us-gaap_PendingLitigationMember_5b26eb4d-debc-4a70-9138-cb7cebd4657b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-roles-2021-01-31.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/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.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="0"/>
  </link:definitionLink>
</link:linkbase>
