<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2025 Workiva-->
<!--r:69286067-21c5-45b7-8029-e94079552245,g:6ae7bcdd-35f0-4ab0-9b64-66a37ad613fb-->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:pega="http://www.pega.com/20250411" xmlns:xbrli="http://www.xbrl.org/2003/instance" attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://www.pega.com/20250411">
  <xs:import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/dei-sub/2024" schemaLocation="https://xbrl.sec.gov/dei/2024/dei-sub-2024.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/ecd-sub/2024" schemaLocation="https://xbrl.sec.gov/ecd/2024/ecd-sub-2024.xsd"/>
  <xs:annotation>
    <xs:appinfo>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="https://content.edgar-online.com/edgar_conv_xbrl/2025/04/11/0001013857-25-000096_pega-20250411_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="https://content.edgar-online.com/edgar_conv_xbrl/2025/04/11/0001013857-25-000096_pega-20250411_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:type="simple"/>
    </xs:appinfo>
  </xs:annotation>
  <xs:element id="pega_AdjustmentToCompensationAmountEquityAwards" abstract="false" name="AdjustmentToCompensationAmountEquityAwards" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
</xs:schema>