Some groups of practitioners seeking professionalization seem to remain stuck in-between the community and professional sectors. Peer support workers in mental health care are a case in point. Peer support workers are increasingly recognized for their unique role as past of multidisciplinary teams, and hired as paid providers. Yet, despite decades of efforts and the support of allies, in most parts of the world, they have not acquired the full professional status they have been pursuing. Based on a longitudinal case study conducted from 2015 to 2024 – involving extensive participant observation, interviews with key actors, and historical documents – we analyze the longstanding struggle of peer support workers to carve out a work jurisdiction within the professional sector of mental health care in the Canadian province of Quebec. Using liminality as a theoretical lens, we investigate how the role of peer support workers in-between the community and professional sectors is creating ambiguity and tensions that might both enable and harm their project. We discuss the theoretical implications of our findings for organizational studies of liminality and professionalization projects.