Background <p>Behavioural physical activity (PA) interventions have shown success among people living with and beyond cancer (LWBC). Intervention delivery typically involves qualified exercise professionals (QEP); however, peer mentors (i.e. active people LWBC) may enhance such interventions as they can provide practical and emotional support from their lived experience. The purpose of this study was to examine the feasibility and acceptability of a peer-delivered PA behaviour change intervention for inactive people LWBC.</p> Methods <p>Inactive people LWBC participated in a 6-week intervention informed by the Multi-process Action Control Framework (M-PAC). Week 1 included a QEP-hosted webinar educating participants on how to meet cancer-specific PA guidelines. In weeks 2–6, participants met weekly with a peer mentor to discuss behaviour change strategies. Feasibility and acceptability were assessed with enrollment, retention, and adherence rates, intervention satisfaction and semi-structured interviews. Secondary outcomes (i.e. PA, quality of life, M-PAC constructs) were self-reported.</p> Results <p>Participants (<i>N</i> = 15; <i>M</i>_age = 53.6 ± 11.6; 73.3% female) were primarily diagnosed with breast (60.0%) or prostate (13.3%) cancer. Enrollment, retention and adherence rates were 58.1%, 83.3% and 100%, respectively. Participants and peer mentors (<i>N</i> = 11) both reported high satisfaction with the intervention (range: 3.5 to 4.8 of 5 points). Qualitative results largely supported quantitative reports of satisfaction, indicating some areas of intervention refinement. Participants increased self-reported moderate-to-vigorous PA (<i>M</i>_diff = 104.0&#xa0;min/week), with 73.3% meeting PA guidelines at post-intervention.</p> Conclusion <p>Meeting all predetermined success criteria, the peer-led intervention was feasible for both participants and peer mentors. Larger, randomized controlled trials are needed to determine intervention efficacy and mechanisms of action.</p>