This study was conducted to examine the construction of social identity among mental health experts by experience working in Finnish municipal mental healthcare services. The construction of social identity is approached as an ongoing lifelong process that is significantly affected by lived experiences with mental health problems and recovery from them. The research data consist of focus group discussions, and the analysis is based on a thematic design that is initially material-driven. As a result, four categories are formed to describe the effect of acting as an expert by experience on social identity and the importance of the issue. Experts by experience have to consider profound questions about their identity and future in their new life situation. The individual meanings of acting as an expert by experience are considered particularly important. The support provided by group members builds confidence in one’s chances of success and thereby supports the development of social identity. Social identities of experts by experience are partially built in encounters with professionals representing the mental health care system. This creates opportunities for new roles for those who act as experts by experience.