Background: Stigma attached to having an intellectual disability has negative implications for the social identities and inclusion of people with intellectual disability. Aim: The study explored the effects of membership of independent self-advocacy groups on the social identity of people with intellectual disability. Method: Using a constructivist grounded theory methodology, semi-structured interviews were conducted with 25 members of six self-advocacy groups which varied in size, resources, location and policy context: two based in the Australian states of Victoria and Tasmania and four in the UK. Results: Collegiality, ownership and control by members characterized groups. They gave members opportunities for paid or voluntary work, skill development and friendship which contributed to their confidence and engagement with life. Possibilities for new more positive identities such as being an expert, a business-like person, a self-advocate and an independent person were opened up. Self-advocacy is an important means of furthering social inclusion of people with intellectual disability.