BACKGROUND: Peer support is increasingly acknowledged as an integral part of mental health services around the world. However, most research on peer support comes from high-income countries, with little attention to similarities and differences between different settings and how these affect implementation. Mental health workers have an important role to play in integrating formal peer support into statutory services, and their attitudes toward peer support can represent either a barrier to or facilitator of successful implementation. Thus, this study investigates mental health workers' attitudes toward peer support across a range of high- (Germany, Israel), middle- (India), and low-income country (Tanzania, Uganda) settings. METHODS: Six focus groups were conducted in Ulm and Hamburg (Germany), Butabika (Uganda), Dar es Salaam (Tanzania), Be'er Sheva (Israel), and Ahmedabad, Gujarat (India) with a total of 35 participants. Transcripts were analyzed using thematic content analysis. RESULTS: Participants across the study sites demonstrated overall positive attitudes towards peer support in mental health care, although some concerns were raised on potentially harmful effects of peer support such as negative role modelling and giving inadequate advice to service users. Notably, mental health workers from low- and middle-income countries described peer support workers as bridge-builders and emphasized the mutual benefits of peer support. Mental health workers' views on peer support workers' roles and role boundaries differed between sites. In some settings, mental health workers strongly agreed on the need for role clarity, whereas in others, mental health workers expressed mixed views, with some preferring blurred role boundaries. Regarding collaboration, mental health workers described peer support workers as supporters and utilizers, equal partners or emphasized a need for trust and commitment. CONCLUSIONS: Mental health workers' attitudes toward peer support workers were positive overall, but they also varied depending on local context, resources and previous experiences with peer support. This affected their conceptions of peer support workers' roles, role clarity, and collaboration. This study demonstrated that reconciling the need for local adaptations and safeguarding the core values of peer support is necessary and possible, especially when the implementation of recovery-oriented interventions such as peer support is accelerating worldwide.