Social inclusion means being able to participate in activities valued within one’s community or wider society as one would wish. People with severe mental illness (i.e., psychoses, bipolar disorder, and severe depression) experience some of the highest rates of social exclusion compared to people with other disabilities. This is the case regardless of the availability of specialist mental health services. Therefore, questions arise about the extent to which mental health services can and do prioritize social inclusion as a goal of service provision, and what strategies are needed outside of mental health services, at the levels of legislation and policy, statutory services, and civil society. In this paper we consider what social inclusion means in different cultures and contexts, since the value attached to different activities varies by culture and by life stage and gender. We discuss the subjective impact of low levels of social inclusion in terms of loneliness, and the evidence base for interventions to address it. We then turn to strategies to increase observable forms of social inclusion, considering them at the levels of legislation, services and other community assets. While evidence for some interventions is largely based on the Global North, we use evidence and examples from the Global South to the extent that we have found them. We also consider the predominant frameworks for social inclusion used in health services, followed by alternatives that may offer a more empowering approach to social inclusion for some people. We then describe strategies to reduce social exclusion through interventions to address stigma and discrimination, directed at key target groups or at population level. We make recommendations for policy makers, researchers, health professionals, and advocates based on the evidence and examples we have found, covering various forms of legislation, services and mental health research. Our conclusions identify the next steps for interventions, including development, evaluation, implementation or modification for better contextual adaptation.