Over the past two decades, recidivism rates have remained relatively stable, leading practitioners to explore innovative reentry solutions. One reentry model, based on the concept of peer mentorship, has received renewed attention. Unfortunately, little is known about which peer characteristics make mentors most effective in a prison setting. This study uses participant observation and semi-structured interviews, embedded with survey questions, to understand which “peer” characteristics prison staff, peer mentors, and mentees perceive as the most important. Analysis of survey data also suggests that a history of incarceration is perceived as the most important characteristic for peer mentors in a reentry context. Additionally, the qualitative analysis reveals that mentors need to be perceived as credible to be effective role models for reentry. This credibility was almost exclusively linked to a lived experience of incarceration. Peer mentorship remains a viable option for improving reentry outcomes, but hiring the appropriate, credible peers is essential for effective implementation.