To tackle complex sustainability problems, science and practice must join forces and interact in the processes of knowledge co-production. This central claim of sustainability science requires all actors to do more than simply participate in a workshop or carry out traditional research. It is essential to provide clarity to actors about the roles to adopt in these processes, especially in terms of planning collaborations—with whom, when, and how. Therefore, in this paper we identify, describe, and discuss 15 roles for actors involved in such processes. We undertook a systematic literature review to identify papers with precise descriptions of transdisciplinary (td) and transformative (tf) research processes. We focused on the common occurrence of activities undertaken by actors by applying 72 activity codes a total of 549 times. Subclusters of activities were identified by means of a hierarchical cluster analysis and these were condensed into 15 roles. The roles can be categorised in four activity realms: field, academia, boundary management, and knowledge co-production. The roles of the Data Supplier, the Field Expert, and the Application Expert are adopted by actors who originate from the field, whereas the roles of the Scientific Analyst and the Knowledge Collector are primarily adopted by researchers. Furthermore, we identified 10 roles within the activity realms of the knowledge co-production process and boundary management. The high number and diversity of roles, especially in the realm of boundary management, reveals the importance of a comprehensive approach to coordination, communication, and process design.