The importance of integrating history into mathematics education is widely recognised in the literature and advocated in curricula worldwide, including in China. However, under the influence of the long-standing centrally designed curricula, teachers in China are accustomed to content- and teacher-centred examination-driven teaching practices. Adopting a life story approach, this paper reports the case of a mathematics teacher who integrated history into her mathematics teaching during the initial two years of her teaching in a Shanghai high school. The agentic perspective adopted in the study allows us to focus on how the teacher's agency was enacted and achieved when engaging in teaching practices. Our findings reveal the roles played by personal qualities, prior experiences, and the structure and culture of schooling in the teacher's agency in integrating history into teaching under a dominant performance-driven context. Implications of the results for integrating history into teaching in restricted contexts are then discussed.