Introduction: Homelessness and mental illness are associated with poor service engagement, health and health service use outcomes. Existing literature suggests that financial incentives may effectively support service engagement of this population, but studies investigating key stakeholder perspectives are lacking. This study aimed to elicit, using qualitative methods, nuanced service user and provider experiences by using financial incentives to support service engagement among adults experiencing homelessness and mental illness. Methods: This qualitative study is part of a larger mixed-methods pragmatic trial of financial incentives (Coordinated Access to Care for the Homeless-Financial Incentives [CATCH-FI]) within a community-based brief case management programme (CATCH) in Toronto, Ontario. Twenty-two CATCH-FI participants were purposefully recruited to participate in in-depth, semi-structured interviews; five CATCH service providers participated in a focus group and seven key informants in individual interviews. Data collection occurred between April 2019 and December 2020. All interviews and the focus group were audio-recorded and transcribed. Topic guides prompted participant perspectives on and experiences of using financial incentives to support engagement, health and well-being. Grounded theory and inductive thematic analysis guided coding and interpretation of transcripts. Triangulation and member-checking enhanced the analytical rigour and validity of findings.Results: CATCH service providers, key informants and subgroup of CATCH-FI participants perceived financial incentives to directly facilitate service engagement.