This article presents a systematic review of a substantial body of literature that considers the ways in which the concept of teacher identity has been used to understand and explore teachers' professional lives. The aim of the review was to go beyond the limitations of specific areas of teachers' practice to explore the broad and rich field of teachers' professional lives. Drawing on 412 articles from 2000–2021, the review demonstrates the growth in teacher identity research, particularly since 2010. Results from the review are categorised into seven thematic groups that span key areas related to teachers' professional lives: (1) Models and frameworks of professional lives; (2) Narratives of professional lives; (3) Becoming a teacher; (4) Contexts; (5) Communities; (6) Change, transition and conflict; and (7) Subject specialisms. The review reveals gaps in teacher identity research, such as: few research studies from Global South countries; a limited number of studies focusing on non-core curriculum subjects, including arts, history, geography and physical education; fewer studies focusing on primary school and early years teacher identities; and a divide between identity scholarship and research, and policy and practice. The article concludes with a call for teacher identity research to be expanded and broadened with the aim to facilitate the progress of identity work in scholarship, policy and practice. Context and implications Rationale for this study In the context of a growing body of research on teacher identity, particularly in the last decade, there remains a paucity of identity-focused systematic reviews. Existing systematic reviews tend to focus on specific fields such as subject specialisms, teacher education and beginning teachers. However, far fewer reviews span the broader field of teachers' professional lives; this article responds to this gap in the literature. Why the new findings matter The findings from this review are important in highlighting the most commonly explored areas in teacher identity research as it relates to teachers' professional lives. As such, the findings can inform policy and practice for teacher education and professional development at local, national and international scales. The findings also highlight gaps in the literature and the implications this may have on teacher identity scholarship. Implications for educational researchers and educators Firstly, educational researchers can identify key themes arising from existing teacher identity research studies. This can help them to focus on specific areas that would benefit from further research as well as providing them with a single space from which to draw on the existing corpus of research studies. Secondly, teacher identity research is important for the professional lives and practice of educators and this review provides educators with an opportunity to understand the teacher identity scholarly landscape and, in turn, apply findings from the research to their own professional practice.