Learning to teach is conceptualized as a complex process of identity development. To address this process, this study explored Prospective Teachers’ (PTs) professional identity development at different stages of learning to teach within a four-year Second Language (L2) initial teacher education program. Participating in a sequential explanatory mixed-methods approach, 140 PTs filled out the English language teacher professional identity questionnaire three times: at the end of the second year, third year, and fourth year. Then, after each round of the questionnaire administration, 12 PTs were asked to participate in the interview phase to gain further insight into the participants’ professional identity development. Three separate sets of Freidman test and grounded theory were employed to evaluate the questionnaire and interview data, respectively. The results of both quantitative and qualitative data analyses revealed that the second-year PTs’ language awareness had a major contribution to the enactment of collective identity of language analyst and language user roles as part of their professional identity. Teaching practicum experiences also helped the third-year PTs develop a sense of belonging to the school community by aligning themselves with its rules and policies, which helped them develop their professional identity in a prescribed manner, informing institutionally situated identity of formal teachers. The fourth-year PTs’ identification of themselves with regard to their prospective learners’ needs was also the identity development observed in the form of learner-oriented attitude toward learners as whole persons, all conducive to imagined future identity of needs analysts. The results and implications are further discussed.