ObjectivesTo move beyond professionalism as a measurable competency, medical educators have highlighted the importance of forming a professional identity, in which learners come to ‘think, act, and feel like physicians’. This socialisation process is known as professional identity formation (PIF). Few empirical studies on PIF in residency have been undertaken. None of these studies focused on PIF during the full length of GP training as well as the interplay of concurrent socialising factors. Understanding the socialisation process involved in the development of a resident’s professional identity and the roles of influencing factors and their change over time could add to a more purposeful approach to PIF. Therefore, we aimed to investigate the process of PIF during the full length of General Practice (GP) training and which factors residents perceive as influential.DesignA qualitative descriptive study employing focus group interviews.SettingFour GP training institutes across the Netherlands.ParticipantsNinety-two GP residents in their final training year participated in 12 focus group interviews.ResultsStudy findings indicated that identity formation occurs primarily in the workplace, as residents move from doing to becoming and negotiate perceived norms. A tapestry of interrelated influencing factors—most prominently clinical experiences, clinical supervisors and self-assessments—changed over time and were felt to exert their influence predominantly in the workplace.ConclusionsThis study provides deeper empirical insights into PIF during GP residency. Doing the work of a GP exerted a pivotal influence on residents’ shift from doing as a GP to thinking, acting and feeling like a GP, that is, becoming a GP. Clinical supervisors are of utmost importance as role models and coaches in creating an environment that supports residents’ PIF. Implications for practice include faculty development initiatives to help supervisors be aware of how they can perform their various roles across different PIF stages.