The current study investigated the Iranian Teaching English as a Foreign language (TEFL) Ph.D. candidates’ (TPCs) professional identity development during the TEFL Ph.D. education program (TPEP). Applying a mixed-method design, the current study used two kinds of instruments: a four-point, Likert-scale, a researcher-made questionnaire on TPCs’ professional identity development, and the semi-structured interviews. First, the survey was mailed to ۸۰ university instructors. Then, to yield an in-depth understanding of how TPCs develop their professional identity, TPCs with more than ۱۰ years of intensive experience were asked to participate in the interview. Following the quantitative data analysis, the qualitative data obtained through semi-structured interviews were analyzed using descriptive qualitative content analysis techniques. The results indicated that the majority of the participants believed that TPEP caused them to gain social legitimation from their community of practice, to get socialized to their global community, and raised their social status; therefore, they believed that not only professional but also personal development took place. Furthermore, it developed their pedagogical knowledge; however, it created small changes in the likelihood of TPCs’ career advancement and led to a small increase in their job satisfaction and security. The findings of the study can have some pedagogical implications for teacher education programs in that they can be used to emphasize their strengths, eliminate their weaknesses, and incorporate ample opportunities for TPCs’ reflection on their current and aspiring professional identities and improve their performance in classes.