There is a growing number of studies evaluating the impact of positive psychology interventions (PPI’s) in people with severe mental illnesses (SMI). The results of these studies have not been quantitatively reviewed yet. In this study, we conduct a meta-analysis on the effects of PPI’s on mental health in people with SMI across studies. Sixteen studies are included (nine RCTs), representing 729 patients. Meta-analyses were performed for well-being as the primary outcome at post-treatment. We found no significant effects on both well-being en psychopathology for the PPI’s in comparison with the control conditions. Within-group effects revealed a moderate effect (Hedge’s g = 0.40) on well-being and a large effect on psychopathology (g = 0.70). Though there is at present no evidence that PPIs are more effective in comparison with other active interventions, our findings demonstrated that people with SMI do benefit from PPIs in terms of enhancement of mental health.