ABSTRACTSubstantial literature has focused on language teacher agency and identity in relation to learners in classrooms. Relatively little research exists regarding the nature of language teacher identity shaped by contextual factors brought on by the internationalization of education. To address the gap in the literature, this study explored how student teachers in a TESOL program negotiate their language teacher agency and identity in the ecosystems of an internationalized institution of higher education while contributing to different ESL programs. While pursuing an MA degree in TESOL with a teaching opportunity at an Intensive English program for non‐matriculating students or an ESL service program for pathway program students at a US university, seven student teachers participated in semi‐structured interviews, which were triangulated with the student teachers’ portfolios of lesson plans and reflection papers. The analysis demonstrated the student teachers’ agentic beliefs, choices, and practices in relation to contextual factors in the nested ecosystems of internationalized higher education, such as international students’ needs in the microsystem, training opportunities in the mesosystem, institutional policy and practice in the exosystem, and broad cultural norms in relation to language education in the macrosystem.