Defining professional identity has long been a contested matter, even more so in social work with ongoing questions about our professional status. To address these questions, this article explores how professional identity is theorized, defined, and/or measured in peer-reviewed social work literature by reporting on a subset of findings from a scoping review. The search protocol produced a total dataset of ninety-one peer-reviewed articles, sixty-six of which specified theory and/or a definition and/or scale indicators related to professional identity. Descriptive analysis was undertaken on bibliographic data from the sixty-six papers, as well as thematic analysis on key sections related to definitions of and theories informing professional identity in social work. Descriptive analysis revealed that most studies were qualitative, and the countries of focus were centred in China and Euro-Western contexts. Thematic analysis produced four themes that are used to propose a comprehensive and multidimensional definition of professional identity for social work, which has implications for social work associations, educators, and practitioners. Recommendations for future research incorporating this definition are also highlighted, especially opportunities for international comparative research. For decades, defining professional identity in social work has been a challenging exercise. Our article is the first to offer a new and comprehensive definition of professional identity for social work. We produced our definition by undertaking a scoping literature review to explore how professional identity has been defined, theorized, and measured in social work since 1999. Our review process produced sixty-six peer-reviewed articles for analysis. Most of the articles were empirical studies that had used qualitative methods to explore professional identity. Many of the articles were conducted in China and Western countries. Thematic analysis was undertaken, and four interconnecting themes emerged from the definitions of professional identity related to socialization, shared characteristics, professional structures, and feelings of belonging and commitment. These themes form the basis of our proposed definition of professional identity in social work and demonstrate how professional identity is a multidimensional concept. We conclude our article by outlining opportunities for future research that incorporates this definition, especially for studies that compare professional identities across different countries. Our work brings much needed clarity to a contested area by improving how professional identity is defined in social work, which has implications for social work associations, educators, practitioners, and research.