Background <p>The engagement of people with lived/living experience and caregivers in the research process can have many benefits for research and all those involved. However, research engagement settings need to be accessible to ensure that people with lived/living experience and caregivers can contribute fully to the research process, including in mental health and substance use health research contexts. This qualitative descriptive study aimed to understand the perspectives of people with lived/living experience and caregivers with regards to accessibility needs in contexts of engagement in mental health and substance use health research.</p> Method <p>A sample of 20 people with lived/living experience and caregivers with research engagement experience in the mental health and substance use health sector participated in one of five focus group discussions. Discussions were recorded, transcribed verbatim, and analyzed using codebook thematic analysis. A Lived/Living Experience and Caregiver Working Group supported all stages of the project, from design to reporting.</p> Results <p>Four themes were generated from the data: (1) Ongoing and transparent accessibility processes. (2) Offering a range of supports. (3) Allowing flexible ways to contribute. (4) Providing fair compensation. Themes are supported by subthemes and described with illustrative quotes.</p> Conclusions <p>Ensuring that engagement is accessible and that appropriate accessibility supports are provided is essential to ensuring an authentic, meaningful engagement experience. This is an ongoing process that should be considered throughout the lifespan of the research project. By planning for accessibility early and throughout the project, research teams can help ensure that people with lived/living experience and caregivers can contribute meaningfully to the research to the best of their ability and without undue hardship.</p>