This study investigated how three Korean ESL students constructed their writer identity in narrative and argumentative genres of writing. For this purpose, the qualitative data collected from interviews, observations and written documents for eight weeks were analyzed according to a social constructionist perspective as a philosophical framework and Ivanič’s approach to systemic functional linguistics as an analytic method. The results showed that the participants constructed a confident identity in narrative writing whereas they identified themselves with a less-confident writer in an argumentative genre. Accordingly, they adopted different strategies for the difficulties they were confronted with in two genres. In addition, while narrative essays showed their ownership of Korean culture as a sojourner in the U.S., argumentative essays revealed their ambivalent identity in an academic context. These findings shed light on the importance of a narrative writing task as a stepping stone for academic writing by empowering an L2 writer in terms of constructing an authoritative voice.