Background: We conducted feasibility testing of a novel peer mentoring intervention addressing self-awareness and proactive coping for young adults with intellectual and developmental disabilities and co-occurring mental health conditions. Aligned with regulatory flexibility theory, we hypothesised that if young adults with intellectual and developmental disabilities and co-occurring mental health conditions learned a range of coping strategies, then they would have greater self-efficacy for managing their emotions and, subsequently, decreased mental health symptoms. Methods: Five participants (M[subscript age]: 20, range: 16-22) were mentored by another young adult with intellectual and developmental disabilities and co-occurring mental health conditions for 10 sessions. Feasibility data collected included the following: enrollment data, attendance rates, participant and parent member experiences and observation of change (via post-intervention interviews), and mentoring satisfaction via a mentoring questionnaire (range 15-60). Findings: Our enrolment rate was 16%. Mentoring was acceptable to young adults, as demonstrated by high attendance rates (98% of sessions attended), mentoring questionnaire responses (M=49.4) and feedback describing the intervention as enjoyable and mentors as "nice," and "understanding." Participants and parents reported potential change in self-efficacy for managing emotions (proximal outcome), use of coping strategies and self-awareness of needs, but few changes in mental health symptoms (distal outcomes). Conclusions: The peer mentoring intervention was feasible and acceptable for young adults with intellectual and developmental disabilities and co-occurring mental health conditions. Results suggest a longer intervention duration may be necessary to elicit changes in mental health symptoms. To enhance feasibility, different recruitment strategies should be considered.