Calls for transformative change and participatory modes of knowledge production demand researchers to assume new roles. This paper synthesizes the literature on knowledge co-production and researcher roles to explore challenges for researchers involved in transdisciplinary environmental management projects. Our research methods combine a scoping review and reflections on personal experiences with three transdisciplinary projects. To conceptualize researcher roles in transdisciplinary knowledge co-production, we distinguish between three spaces: knowledge, formal policy, and stakeholder. Knowledge co-production requires collaboration between actors from different spaces and integration of diverse knowledge sources and types. Depending on whether researchers adopt knowledge-oriented, change-oriented or intermediating roles, they will experience different challenges. When researchers combine knowledge development with change-oriented and/or intermediating roles, they encounter new challenges, such as, maintaining independence or objectivity. To assist researchers in transdisciplinary projects, we conclude with a checklist of four elements to reflect upon: orientation, norms and values, expectations and resources.