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. 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. Regression analyses showed that unemployment (β=-.16, p<.001), lack of social support (β=-.20, p<.001), distressing beliefs (β=-.12, p=.004), and poorer coping (β=-.43, p<.001) were associated with reduced SWB, together accounting for 43% of the variance in well-being, F(5, 392)=58.42, p<.001; mean SWB=39.09, SD=11.61. This study provides preliminary insights into the determinants of SWB in a large sample of people with psychosis. Improving employability, social interactions, coping strategies, and psychotic symptoms may improve SWB. Further longitudinal investigation will determine the potential value of preferentially targeting these areas in therapy to meet national requirements to prioritize well-being outcomes. Average well-being in people with psychosis was lower than SWB previously reported for the general population. Unemployment, lack of social support, poorer coping, and distressing beliefs were all associated with lower levels of well-being in people with psychosis. Psychological interventions targeting the positive symptoms of psychosis may impact on well-being. Greater focus on promoting social contact and inclusion and facilitating a return to employment may further improve well-being outcomes following psychological intervention. The cross-sectional design of the study does not allow for firm conclusions about the causal relationship between well-being and associated factors in psychosis. The study was carried out within a particular service context, and the findings need replicating before they can be considered to be generalizable outside this setting.