This systematic review synthesizes 51 empirical studies on non-university-based teacher educators' (NUBTEs) professional learning published between 2000 and 2022. The results show that NUBTEs strive to develop a host of professional qualities that enable them to support preservice and in-service teachers' growth through formal and informal learning experiences. The reviewed studies are predominantly qualitative research and have produced context-specific knowledge about NUBTEs' professional learning, but cross-contextual and large-scale empirical evidence is currently scarce. These findings suggest theoretical, practical, and methodological implications for advancing the research field of teacher educators' professional learning.