Previous longitudinal studies have explored the developmental mechanisms of non-suicidal self-injury (NSSI) and suicidal ideation (SI) in adolescents and primarily focused on variable levels rather than trajectories (e.g., intercepts and slopes). The present study aimed to explore the developmental trajectories of NSSI and SI among Chinese adolescents, emphasizing the predictive roles of fear of negative evaluations (FNE) and thwarted belongingness (TB) on these trajectories from an interpersonal perspective. The latent growth model was incorporated to construct a mediation model of FNE, TB, NSSI, and SI. A total of 515 adolescents (M