This article reports a mixed methods study on the contribution of various aspects of pre-service student teachers' learning in initial teacher education (ITE) to their professional competence in a Five-year Bachelor of Education Programme in Hong Kong. Special attention is given to how student teachers' non-formal learning in higher education contributes to their professional competence, an under-researched area in teacher education. A total of 282 student teachers participated in the quantitative survey, 18 of whom were interviewed. Although "Undergraduate Learning Experience: Formal Learning and Non-formal Learning" was not the most highly rated factor, multiple regression indicated that it was the only ITE professional learning factor that significantly predicted all dimensions of professional competence. This supports the hypothesis that non-formal learning as a part of learning in higher education makes a significant contribution to student teachers' professional competence. The qualitative findings showed that non-formal learning provided opportunities for service learning, co-curricular activities, and student exchange programmes with different objects of engagement. Student teachers constructed pedagogical content knowledge, general pedagogical knowledge, and knowledge of context through hands-on experiences, professional dialogue with practitioners, and observations of others' practice. Such knowledge contributed to their competence in classroom teaching and to work in schools. Implications for ITE are discussed.