Researchers in urban planning are frequently motivated by the desire to facilitate positive social change. In seeking better ways to effect change, the researcher becomes an activist by engaging with social and environmental issues in a meaningful way to solve a problem. It is also often at this nexus where practice and academia meet, where the researcher adopts an activist role. In this paper we argue that activist research requires researchers to place themselves in one of two dominant positionalities or engagement positions: the insider or the outsider, as they join efforts with their research participants and activities. Using four case examples from our own research, we discuss how each positionality influences the production of new knowledge in both practice and theory. We reflect on challenges faced by early-career activist researchers in adopting activist research approaches, highlighting implications for undertaking this type of research in urban planning, and the need for a rethink from current discourses to set a path for a more hopeful future.