Background <p>Peer-provided services play a crucial role in healthcare delivery across health care issues. This study describes the process of implementing a peer navigation program called mentoring and peer support (MAPS) for individuals with serious mental illness (SMI) reentering the community after jail release.</p> Methods <p>In-depth interviews were conducted with four peer navigators, and the 12-item Working Alliance Inventory Scale was used to assess their perspectives on the program. Additionally, 25 administrative documents were reviewed to describe implementation processes. An applied thematic analysis was conducted using the Consolidated Framework for Implementation Research (CFIR).</p> Results <p>Results from qualitative exit interviews, the Working Alliance Inventory survey, and administrative reviews indicate that the MAPS program was feasible, acceptable, and culturally appropriate. However, opinions on its effectiveness were mixed. Peer navigators faced challenges accessing clients in jail due to facility lockdowns and short staffing. They also encountered client skepticism, as some initially mistook them for law enforcement or probation officers. Maintaining post-release contact was difficult due to unreliable phone numbers and unstable housing. Recommendations include aligning jail release times with community service hours, diversifying participant incentives, and employing full-time peer navigators for greater flexibility.</p> Conclusion <p>Peer navigation programs like MAPS hold promise for enhancing mental health service linkage among reentering individuals. Stronger post-release support systems and clearer role definitions to mitigate client distrust would advance implementation. Findings from this study will inform implementation of an adequately powered randomized trial evaluating effectiveness and cost-effectiveness of the MAPS intervention.</p>