The present study examines how L2 graduate writers are socialized into the academic discourse practices of a U.S. graduate school via Graduate Writing Groups (GWGs) sponsored by the university writing center. More specifically, it sheds light on how the discourse and interactions within a peer-based GWG affect L2 graduate writers’ identities, as well as their socialization into academic disciplines and cross-disciplinary academic conventions. Results of the study revealed that unlike the simple portrayal of L2 graduate writers as novices and their enculturation into academia as linear and unidirectional, L2 graduate writers have multi-faceted identities as writers depending on academic task, context, and previous academic literacy experiences. The study suggests that despite the potential challenges inherent in multidisciplinary GWGs, they offer valuable opportunities for L2 graduate writers to enact the identity of disciplinary expert. Furthermore, the peer-based, extracurricular nature of these groups support graduate writers’ socialization into academic discourse communities.