This paper draws on an ethnographic research that examined Taiwanese international students' identity movements before, during, and after their overseas education in Australia. Previous studies on nonnative-English-speaking teachers (NNESTs) studying TESOL in the West focused on the formation of their professional identity before and after the completion of TESOL programs abroad. This study pioneers a model which examines NNESTs' multilayered complexity of identity formation by drawing on the Douglas Fir Group's (2016) multifaceted nature of language learning and teaching and Wenger's (1998) identification and negotiability of identity formation to analyze one Taiwanese student's developing NNEST identity. We found the participant's social life experiences reshaped her professional identity as NNEST. The user experience as a nonnative English speaker prompted her critical reflection on the notion of functional English user and teaching. This notion, shaped by social aspects of learning, was later demonstrated in her teaching practice. The study suggests: 1) that future research includes NNESTs' social aspects of experiences as nonnative English users; 2) that SLA researchers for TESOL programs continue analyzing NNESTs' deficit discourse with transdisciplinary approach.