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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019e088f-b2c6-7d36-aa7f-e9c1fa4fd20e,g:9a3f3813-aea1-4237-b362-377e23348e41-->
<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://riministreet.com/role/Cover" xlink:type="simple" xlink:href="rmni-20260730.xsd#Cover"/>
  <link:definitionLink xlink:role="http://riministreet.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_019e088f-b2c6-790a-b871-92c3ee2f1e6d" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_DocumentInformationTable_019e088f-b2c6-790a-b871-92c3ee2f1e6d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019e088f-b2c6-718c-b74e-d86dc95e2421" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_019e088f-b2c6-790a-b871-92c3ee2f1e6d" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019e088f-b2c6-718c-b74e-d86dc95e2421" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e088f-b2c6-718c-b74e-d86dc95e2421_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019e088f-b2c6-718c-b74e-d86dc95e2421" xlink:to="loc_us-gaap_EquityComponentDomain_019e088f-b2c6-718c-b74e-d86dc95e2421_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019e088f-b2c6-72c7-aac1-787512dbc009" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019e088f-b2c6-718c-b74e-d86dc95e2421" xlink:to="loc_us-gaap_EquityComponentDomain_019e088f-b2c6-72c7-aac1-787512dbc009" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019e088f-b2c6-7c1c-81a4-5ed590b24aee" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019e088f-b2c6-72c7-aac1-787512dbc009" xlink:to="loc_us-gaap_CommonStockMember_019e088f-b2c6-7c1c-81a4-5ed590b24aee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019e088f-b2c6-7b0f-8ca2-8fa80729771f" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_EntityCentralIndexKey_019e088f-b2c6-7b0f-8ca2-8fa80729771f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019e088f-b2c6-71dc-b305-e733476533df" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_AmendmentFlag_019e088f-b2c6-71dc-b305-e733476533df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019e088f-b2c6-70ea-8462-dd9a2e67eb8e" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_DocumentType_019e088f-b2c6-70ea-8462-dd9a2e67eb8e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019e088f-b2c6-72fd-9510-6f239f7b1ce4" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_DocumentPeriodEndDate_019e088f-b2c6-72fd-9510-6f239f7b1ce4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019e088f-b2c6-7d74-94e6-ab1b6012d347" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_EntityRegistrantName_019e088f-b2c6-7d74-94e6-ab1b6012d347" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019e088f-b2c6-70f4-9340-5136161fa758" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019e088f-b2c6-70f4-9340-5136161fa758" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019e088f-b2c6-7997-824d-5ab3855ff95f" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_EntityFileNumber_019e088f-b2c6-7997-824d-5ab3855ff95f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019e088f-b2c6-7bb6-bd2d-337afcd6adb4" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_EntityTaxIdentificationNumber_019e088f-b2c6-7bb6-bd2d-337afcd6adb4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019e088f-b2c6-7884-871c-40c09dce0e35" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_EntityAddressAddressLine1_019e088f-b2c6-7884-871c-40c09dce0e35" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_019e088f-b2c6-725f-82f7-5eea6edd420f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_EntityAddressAddressLine2_019e088f-b2c6-725f-82f7-5eea6edd420f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019e088f-b2c6-7507-af18-97f18004ccdb" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_EntityAddressCityOrTown_019e088f-b2c6-7507-af18-97f18004ccdb" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019e088f-b2c6-7f60-a942-9f557dc97268" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_EntityAddressStateOrProvince_019e088f-b2c6-7f60-a942-9f557dc97268" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019e088f-b2c6-7175-88ae-8017d0ba0204" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_EntityAddressPostalZipCode_019e088f-b2c6-7175-88ae-8017d0ba0204" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019e088f-b2c6-7c27-b734-cc0dc53178c4" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_CityAreaCode_019e088f-b2c6-7c27-b734-cc0dc53178c4" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019e088f-b2c6-7296-abf0-7a73cab85705" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_LocalPhoneNumber_019e088f-b2c6-7296-abf0-7a73cab85705" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_019e088f-b2c6-7113-84cc-6bd31c95a13a" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_WrittenCommunications_019e088f-b2c6-7113-84cc-6bd31c95a13a" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_019e088f-b2c6-7d2b-9eb4-643d0d81a507" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_SolicitingMaterial_019e088f-b2c6-7d2b-9eb4-643d0d81a507" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_019e088f-b2c6-7032-9052-00b8d38751d9" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_PreCommencementTenderOffer_019e088f-b2c6-7032-9052-00b8d38751d9" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_019e088f-b2c6-7558-a0c4-f29724bcb872" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_019e088f-b2c6-7558-a0c4-f29724bcb872" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019e088f-b2c6-7420-9406-ef6c443dbc64" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_Security12bTitle_019e088f-b2c6-7420-9406-ef6c443dbc64" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019e088f-b2c6-7bd5-8e40-361ea394d0ba" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_TradingSymbol_019e088f-b2c6-7bd5-8e40-361ea394d0ba" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019e088f-b2c6-746d-abfe-bc97e753344b" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_SecurityExchangeName_019e088f-b2c6-746d-abfe-bc97e753344b" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019e088f-b2c6-73f4-8ba6-44b00b703b95" 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_019e088f-b2c6-750a-9eb0-1ff78536c56e" xlink:to="loc_dei_EntityEmergingGrowthCompany_019e088f-b2c6-73f4-8ba6-44b00b703b95" xlink:type="arc" order="22"/>
  </link:definitionLink>
</link:linkbase>
