Objectives Improving subjective well-being (SWB) for people with mental health problems is a United Kingdom national health priority and is increasingly important in justifying funding of mental health services. Aside from the economic advantages, maximizing SWB confers obvious individual and clinical benefits for people with severe mental illness, such as psychosis. Gaining a better understanding of well-being and its determinants will enable current evidence-based interventions to be targeted and refined appropriately. This study therefore sought to identify the cross-sectional correlates of SWB in an Improving Access to Psychological Therapies for people with Severe Mental Illness psychosis demonstration site, to inform a future longitudinal investigation. Methods Participants with a psychosis or bipolar spectrum diagnosis referred to the demonstration site (n = 410) rated SWB as part of their initial assessment before starting psychological therapy. Potential influencing factors including age, gender, ethnicity, employment status, illness duration, perceived social support, perceived coping, and psychotic symptoms (voices and beliefs) were also assessed. Results Regression analyses showed that unemployment (β = −.16, p