This study explores "non-native" English teacher identity development, and identity in practice in a multilingual international school in Thailand. Guided by the teacher's personal interpretative framework (Kelchtermans, 1993) and identity-in-practice theory (Varghese et al., 2005), the study employed a narrative inquiry design using life story interviews, classroom observations, and shadowing technique for the data collection. The three "non-native" English teacher participants were purposefully selected. The data were analyzed by using the inductive coding method (Saldaña, 2009), consisting of three analysis steps: open coding, axial coding, and selective coding. The data revealed that teacher identity development was characterized by solid confidence in their "non-native" status and their teaching abilities as English teachers due to professional qualifications, proficiency in English, and teaching experiences. However, it was revealed that their "non-native" status were affected by external factors (parents and colleagues), weakening their self-esteem and job motivation. This study emphasizes the importance of English proficiency level and qualifications in building confidence among non-native English teachers. Additionally, a supportive socio-cultural environment inside the school is key to support their positive identity and maintain their confidence.