English medium instruction (EMI) has now become a ubiquitous education phenomenon due to the driving force of globalization and the prospective socioeconomic benefits associated with English proficiency. Although expanding rapidly in higher education, EMI in secondary education is a much less researched area. Specifically, EMI teachers' agency in the implementation of EMI has remained relatively less known. This study, informed by an extended framework on teacher agency, seeks to investigate how such agency has been manifested while the EMI teachers address various tensions and contradictions in the course of implementing EMI. Drawing on qualitative interviews and classroom observations in an international high school in Shenzhen, China, it reveals that the participants have exhibited moderately high levels of agency by constructing themselves as translanguagers who orchestrate different languages and meaning-making resources, jugglers of the roles of content teachers and L2 teachers, as well as duty-bond multicultural educators who negotiate the international curriculum to accommodate local educational and cultural mandates. The study calls for reconceptualizing EMI as a translanguaging space for the teachers to act as culturally responsive agents qua multilingual educators featuring multiple identities.