Background: Poor social circumstances can induce, exacerbate and prolong symptoms of mental health conditions, while having a mental health condition can also lead to worse social outcomes. Many people with mental health conditions prioritise improvement in social and functional outcomes over reduction in clinical symptoms. Interventions that improve social circumstances in this population should thus be considered a priority for research and policy. Methods: This rapid evidence synthesis reports on randomised controlled trials of interventions to improve social circumstances across eight social domains (Housing and homelessness; money and basic needs; work and education; social isolation and connectedness; family, intimate and caring relationships; victimisation and exploitation; offending; and rights, inclusion and citizenship) in people with mental health conditions. Economic evaluations were also identified. A comprehensive, stepped search approach of the Cochrane library, MEDLINE, Embase, PsycINFO, Web of Science and Scopus was conducted. Results: One systematic review and 102 randomised controlled trials were included. We did not find RCT evidence for interventions to improve family, intimate and caring relationships and only one or two trials for each of improving money and basic needs, victimisation and exploitation, and rights, inclusion and citizenship. Evidence from successful interventions in improving homelessness (Housing First) and employment (Individual Placement and Support) suggests that high-intensity interventions which focus on the desired social outcome and provide comprehensive multidisciplinary support could influence positive change in social circumstances of people with mental health conditions. Objective social isolation could be improved using a range of approaches such as supported socialisation and social skills training but interventions to reduce offending showed few benefits. Studies with cost and cost-effectiveness components were generally supportive of interventions to improve housing and vocational outcomes. More research is needed to ensure that social circumstances accompanied by high risks of further exacerbation of mental health conditions are adequately addressed. Conclusions: Although there is a large body of literature examining how to support some aspects of life for people with mental health conditions, more high-quality evidence is required in other social domains. Integration into mental health services of interventions targeting social circumstances could significantly improve a number of social outcomes.