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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019f397b-f7d4-7219-bf8f-44d8965cc671,g:2966cbdf-3a62-4d84-af95-1b275cb69c0c-->
<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://www.uplandsoftware.com/role/Cover" xlink:type="simple" xlink:href="upld-20260630.xsd#Cover"/>
  <link:definitionLink xlink:role="http://www.uplandsoftware.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_019f397b-f7d5-7274-a9de-157774310ac3" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_DocumentInformationTable_019f397b-f7d5-7274-a9de-157774310ac3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019f397b-f7d5-7da5-88bb-5548ff3861e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_019f397b-f7d5-7274-a9de-157774310ac3" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019f397b-f7d5-7da5-88bb-5548ff3861e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f397b-f7d5-7da5-88bb-5548ff3861e6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f397b-f7d5-7da5-88bb-5548ff3861e6" xlink:to="loc_us-gaap_ClassOfStockDomain_019f397b-f7d5-7da5-88bb-5548ff3861e6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f397b-f7d5-71f1-9479-0b21679bd989" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f397b-f7d5-7da5-88bb-5548ff3861e6" xlink:to="loc_us-gaap_ClassOfStockDomain_019f397b-f7d5-71f1-9479-0b21679bd989" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_upld_CommonStockParValue00001PerShareMember_019f397b-f7d5-708b-b123-5c5c48013e84" xlink:href="upld-20260630.xsd#upld_CommonStockParValue00001PerShareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f397b-f7d5-71f1-9479-0b21679bd989" xlink:to="loc_upld_CommonStockParValue00001PerShareMember_019f397b-f7d5-708b-b123-5c5c48013e84" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_upld_PreferredStockPurchaseRightsMember_019f397b-f7d5-7708-9c4c-2675e22c75c6" xlink:href="upld-20260630.xsd#upld_PreferredStockPurchaseRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f397b-f7d5-71f1-9479-0b21679bd989" xlink:to="loc_upld_PreferredStockPurchaseRightsMember_019f397b-f7d5-7708-9c4c-2675e22c75c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019f397b-f7d5-799c-8cc1-1fd5aec2a0b4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_DocumentType_019f397b-f7d5-799c-8cc1-1fd5aec2a0b4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019f397b-f7d5-7530-9edf-2c74a0fda335" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_DocumentPeriodEndDate_019f397b-f7d5-7530-9edf-2c74a0fda335" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019f397b-f7d5-7a9e-b958-ef4f6a7b6ece" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_EntityRegistrantName_019f397b-f7d5-7a9e-b958-ef4f6a7b6ece" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019f397b-f7d5-7ea8-9603-5aae5d28b907" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019f397b-f7d5-7ea8-9603-5aae5d28b907" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019f397b-f7d5-7b85-a49b-3cb1a970faf0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_EntityFileNumber_019f397b-f7d5-7b85-a49b-3cb1a970faf0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019f397b-f7d5-72b0-93c4-f2d1bd6ab3bd" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_EntityTaxIdentificationNumber_019f397b-f7d5-72b0-93c4-f2d1bd6ab3bd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019f397b-f7d5-74a2-bcbf-23a2518d179d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_EntityAddressAddressLine1_019f397b-f7d5-74a2-bcbf-23a2518d179d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019f397b-f7d5-764c-9d6f-684e7f98d566" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_EntityAddressCityOrTown_019f397b-f7d5-764c-9d6f-684e7f98d566" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019f397b-f7d5-79d9-b23f-673954997d0d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_EntityAddressStateOrProvince_019f397b-f7d5-79d9-b23f-673954997d0d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019f397b-f7d5-7e3a-9db4-797f6376f0ad" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_EntityAddressPostalZipCode_019f397b-f7d5-7e3a-9db4-797f6376f0ad" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019f397b-f7d5-7c1e-abd7-9da18272a354" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_CityAreaCode_019f397b-f7d5-7c1e-abd7-9da18272a354" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019f397b-f7d5-7cd6-ae6c-ddecca993122" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_LocalPhoneNumber_019f397b-f7d5-7cd6-ae6c-ddecca993122" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_019f397b-f7d5-7524-879a-1abc42fe1da0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_WrittenCommunications_019f397b-f7d5-7524-879a-1abc42fe1da0" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_019f397b-f7d5-7b82-8bf6-2f5ed0d9874f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_SolicitingMaterial_019f397b-f7d5-7b82-8bf6-2f5ed0d9874f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_019f397b-f7d5-76df-8b7a-a7f426028809" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_PreCommencementTenderOffer_019f397b-f7d5-76df-8b7a-a7f426028809" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_019f397b-f7d5-7e04-a019-ec0c527dd6dd" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_019f397b-f7d5-7e04-a019-ec0c527dd6dd" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019f397b-f7d5-797b-82dd-c878cdaa8dd7" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_Security12bTitle_019f397b-f7d5-797b-82dd-c878cdaa8dd7" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019f397b-f7d5-78e4-8e85-2c87dc247bb8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_TradingSymbol_019f397b-f7d5-78e4-8e85-2c87dc247bb8" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019f397b-f7d5-7743-878e-f673096d0fd3" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_SecurityExchangeName_019f397b-f7d5-7743-878e-f673096d0fd3" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_NoTradingSymbolFlag_019f397b-f7d5-77b5-8a5b-636e5f02a7ae" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_NoTradingSymbolFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_NoTradingSymbolFlag_019f397b-f7d5-77b5-8a5b-636e5f02a7ae" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019f397b-f7d5-7fe4-be4d-ad9fa794b2c3" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_EntityEmergingGrowthCompany_019f397b-f7d5-7fe4-be4d-ad9fa794b2c3" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019f397b-f7d5-71a6-8cdc-48adff1d1910" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_EntityCentralIndexKey_019f397b-f7d5-71a6-8cdc-48adff1d1910" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019f397b-f7d5-7624-ac79-3eadd34af296" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f397b-f7d5-76fb-a229-db2f6298d391" xlink:to="loc_dei_AmendmentFlag_019f397b-f7d5-7624-ac79-3eadd34af296" xlink:type="arc" order="22"/>
  </link:definitionLink>
</link:linkbase>
