Background The implicit association hypothesis of nonsuicidal self‐injury (NSSI) proposes that individuals who engage in self‐injury develop, over time, strong associations between themselves and NSSI, and their identification with this behavior guides their future selection of NSSI to cope. Prior research has established a relationship between implicit NSSI associations (using an Implicit Association Test for Self‐Injury) and engagement in NSSI. However, previous studies have been small and cross‐sectional, and thus underpowered to examine the nature of this association and the extent to which implicit associations predict the persistence of NSSI. Methods This study builds on previous research in a prospective, longitudinal examination of implicit self‐identification with NSSI in a large sample of middle school students. NSSI behavior and implicit NSSI associations were assessed annually in school at three time points. Results Adolescents who engaged in NSSI exhibited stronger implicit self‐identification with NSSI than adolescents who did not engage in NSSI. Moreover, implicit NSSI identification was stronger among adolescents who engaged in cutting, frequent NSSI, and recent NSSI. A reciprocal association was observed between NSSI frequency and implicit NSSI identification over 1 year. Notably, implicit NSSI identification uniquely and prospectively predicted engagement in NSSI over the subsequent year. Conclusions Implicit self‐identification with NSSI may track both trait‐ and state‐related changes in the behavior and, importantly, may help predict continued engagement in NSSI.