Patient and public involvement (PPI) increasingly features in the shaping, design, and conduct of mental health research. This review identifies and synthesizes evidence of barriers and facilitators of PPI in mental health research within university settings. The search strategy followed PRISMA guidance and involved keyword searches in eight peer reviewed databases, grey literature, hand searching two journals, requests to national mental health organizations, and backwards and forwards citation searching. We included primary mental health studies on patient and public involvement, with data on facilitators and barriers. Data were extracted capturing author, date and country of publication, study aim, participant and research team composition, data collection and analysis methods, and levels of PPI. Quality appraisal was conducted using the CASP Checklist for Qualitative Research, with an additional item on intersectionality. We conducted an inductive thematic analysis, before holding a peer-debriefing session with a lived experience working group. The final dataset included 51 articles that were either of a qualitative design or contained analyzed qualitative data. Barriers and facilitators were grouped around the following themes: the structure of the research environment, organizational culture, and individual needs. Good practice exists, but the wider research environment and power imbalances within universities constrain PPI. For PPI in mental health research to reach its full potential, the redistribution of power, building capacity for all, the provision of safe working environments, and widening inclusion in the research process are necessary. This review involved researchers with lived experience of mental ill health.