For many, professional teacher identities begin to develop purposefully and dynamically during the discussions and activities that happen during formal teacher education. Of course, identity formation begins much earlier in one’s lifetime and is influenced by variables such as biographic and cultural background, as well as life experiences. This study aims to explore the narrated identities of L1 and L2 English-speaking TESOL student teachers undertaking an MA TESOL programme at an Irish university. The data from questionnaires and focus groups, analysed through thematic corpus-based discourse analysis, reveal that three major factors contribute to the formation of the professional identities of the TESOL student teachers. These are (1) cultural identity; (2) linguistic identity; and (3) status as student teachers. Discussions highlight the specific details of each from the point of view of both L1 and L2 English-speaking student teachers. The conclusion suggests future pathways for the critical exploration of identity-related issues as a key imperative for student teachers during teacher-education programmes.