BackgroundThere is growing recognition that engaging people with lived experience (PWLE) in mental health and substance use research improves the quality of the research in terms of relevance to the population and the feasibility of the work. Engagement also provides positive opportunities for research teams and the PWLE engaged. However, there are many gaps in the research on PWLE engagement. This scoping review synthesizes the gaps in the implementation of PWLE engagement and in the research on engagement as presented by research teams engaging PWLE in their work.MethodA systematic electronic database search was conducted in 2022 for published articles on PWLE engagement in mental health and substance use research. Potential articles were screened for relevance. The search led to 49 final articles included in the review. The 49 articles were then coded using codebook thematic analysis to answer two research questions: (1) What are the research evidence gaps regarding the engagement of PWLE in mental health and substance use research?; and (2) What are the gaps in implementing PWLE engagement in mental health and substance use research? PWLE were engaged in the conduct of this review.ResultsResults showed that research evidence gaps include further work on conceptualizing engagement; developing resources, tools, and practice recommendations to support research teams; increasing diversity in evaluations of engagement; and evaluating engagement, including its impact on the research, on PWLE, and on researchers. Implementation gaps included several broader institutional gaps and gaps in the day-to-day practice of engagement.ConclusionsDespite progress in PWLE engagement in mental health and substance use research in recent years, research evidence and implementation gaps remain. Research teams are encouraged to consider these gaps and conduct research and implementation activities to address them in a rigorous manner.