Teachers' professional identity is multifaceted and fluctuating, and while it is formally developed during initial teacher preparation, it is influenced by experiences before and beyond teaching programmes. The aim of this paper is to investigate the extent to which a module on language curriculum development may influence the professional identity formation of international and UK student-teachers enrolled in a master's programme in teaching English to speakers of other languages at a UK university. The study was carried out with 30 student-teachers in 2021, and data were collected from an ecological perspective as data sets came from the regular module delivery. Findings show that the student-teachers articulated four spheres of professional identity. Located in the past, the language learner identity helped them reflect on good practices. Their present student-teacher identity was characterised by their acknowledgement of language education as a research-informed area. Drawing on these two spheres, they displayed two future spheres of professional identity: teacher identity and curriculum developer identity. The latter demonstrates that the module not only enabled the participants to imagine a new career path but also helped them reflect on their anticipatory agency and self-efficacy.