Service user involvement in mental health research is on the international political agenda, for example mirrored by an emphasis on user involvement in funding of research. The idea is that service users contribute with their lived experiences of mental distress to the research process and thereby heighten the quality and relevance of the research. The purpose of this scoping review was to identify and evaluate empirical research of how mental health service users actually partake in collaborative research processes and to summarize this research in dialogue with mental health user-researchers. The review included 32 studies. Main findings indicated that actual involvement of service user-researchers in research processes encompassed a complex set of precarious negotiation practices, where academics and service user-researchers were positioned and positioned themselves in alternative ways. The review accounts for how mental health service users were involved in collaborative research processes. The extracted themes concerned: (i) Expectations of research processes, (ii) Contribution to research processes, and (iii) Training and learning from research processes. The study reveals that collaborative research in mental health requires changes to traditional research practices to create and support genuine collaborative partnerships and thereby avoid tokenism and power inequalities.