INTRODUCTION: There is a move towards engaging people with lived experience and families (PWLE/F)-also referred to as PWLE/F engagement-in mental health and/or substance use research. However, PWLE/F engagement is inadequately reported on in mental health and/or substance use research papers. OBJECTIVE: To understand what PWLE/F and researchers perceive are important components to report on related to engagement in mental health and/or substance use research. METHODS: This study included a qualitative description study underpinned by pragmatism. Data were collected through virtual interviews with 13 PWLE/F and 12 researchers across Canada and analysed using template analysis. The results were used to develop a reporting guidance document for engagement in mental health and/or substance use research. RESULTS: The results from the template analysis were structured through the following themes: (1) establishing the need for a guidance document
(2) aspects of engagement to report and reflect on
(3) guidance around co-authorship with PWLE/F
(4) practical tips for reporting on engagement and (5) considerations for journals. Participants identified a need for tailored guidance that is flexible and reflective, yet can promote transparency, accountability and learning in the field. A reporting guidance document was developed for engagement in mental health and/or substance use research that balances flexibility and standardisation while incorporating reflection into reporting. Guidance around co-authorship with PWLE/F partners was also included. CONCLUSION: The guidance document is intended to be used as a roadmap to help guide authors to meaningfully write about engagement without the rigid boundaries of a reporting guideline. We encourage research teams that engage PWLE/F in mental health and/or substance use research to consider using the guidance document as they write up their work. PATIENT AND PUBLIC INVOLVEMENT: PWLE/F members were engaged throughout the study from conception to manuscript production. This included a PWLE partner on the doctoral committee and a Lived Experience Advisory Group consisting of two PWLE and one family partner.