This study aimed to investigate the significance of informal learning contexts in physical education (PE) student teachers’ professional identity construction. It addressed two research questions: How do informal learning contexts contribute to the construction of PE student teachers’ professional identity? What forms of relationships can be identified between the informal and formal contexts of learning in PE student teachers’ professional identity construction? The data consisted of 20 semi-structured interviews with PE student teachers during the final teaching practice period. The data were analysed using structural and pattern coding methods. The analysis revealed that informal learning contexts contributed to three elements of professional identity construction: professional ambitions, professional values and principles, and professional knowledge and competencies. Three distinct forms of relationships between informal and formal learning contexts in the construction of professional identity were also discovered: complementary, reconstructive and disconnected. Informal learning contexts appear highly influential in the construction of professional identity. The results also point towards a holistic notion of professional identity, where professional and personal aspects of identity merge and overlap in the construction of professional identity.