This article investigates the development of teachers’ professional identity during and after engaging in research at a Turkish university, which promotes action research as a key professional development strategy for language teachers. The teachers in this study carried out a process of engaging in research over four years, which presented an opportunity to investigate the development of their professional identities. The results may inform other contexts across the world where the concept of teachers engaging in research is gaining momentum. Finally, we discuss insights into how the professional identity of these teachers developed through action research.