This article offers a scoping review and thematic synthesis of qualitative research on the relationship between precarious employment and mental health. Systematic searches of primary qualitative research in western economies, focused on insecure contracts and a broad conceptualisation of mental health, identified 32 studies. Thematic synthesis revealed four core experiences of precarious employment: financial instability, temporal uncertainty, marginal status and employment insecurity, each connected with multiple, interrelated experiences/responses at four thematic levels: economic, socio-relational, behavioural and physical, leading to negative mental health effects. Reported mental health outcomes could be predominantly understood as reductions in ‘positive mental health’. Findings are theoretically located in models of work-family conflict and latent deprivation; insecure work constrains access to benefits of time structure, social contacts, social purposes, status and identity, which correlate with psychological wellbeing. Frequently failing also to provide the manifest (financial) benefits of work, insecure employment poses mental health risks on both fronts.