Background: Young adults with intellectual/developmental disabilities and co-occurring mental health conditions (IDD-MH) experience significant mental health disparities. Barriers to services include transportation and stigma associated with services. Peer mentoring (PM) may be one solution to these barriers. Methods: We conducted exploratory research to develop a PM intervention for young adults with IDD-MH by partnering with 3 young adults with IDD-MH and a seven-member advisory board. In addition, we conducted focus groups with mental health clinicians (n = 10), peer providers (n = 9), and transition specialists (n = 20) to identify the desired PM outcomes and features and content that may facilitate these outcomes. Results: Prioritized outcome: identifying and utilizing leisure activities as coping strategies. PM features: mentors should use relationship- and outcome-driven actions to operationalize a mentee-centred approach. Features and content considerations: safety, mentor matching, degree of structure, mentor training and support, and collaboration with mentees' support teams. Discussion: Findings are aligned with previous research on PM. [This article was co-authored by the Young Adult Mental Health/Peer Mentoring Research Team.]