This exploratory study conducted a thematic analysis of the process of becoming a supervisor, using data collected from individual interviews. The results show that supervisors’ professional development process follows rules of thumb and lacks structure. The meaning of supervision is rarely constructed in terms of professional identity. Supervisors progress in the process of role impact, imbalance, adjustment, and transformation. They move towards developing professional identity shifting from administration to professional education functions, from administrative processors to managers, and from identification with social workers to supervisors. Furthermore, the transformation of a supervisor’s professional identity cannot be completed automatically. Sufficient professional supervision and support must be provided at the critical moments of transformation. This study contributes to understanding of the development of supervisory professional identity. It emphasizes the need to develop professional training centered on supervisory professional identity.