Introduction: While dysfunctional family processes are recognized risk factors for adolescent smartphone addiction, existing research often focuses on isolated factors and leaves longitudinal mechanisms unclear. The development of emotion-related impulsivity has been suggested as a potential mechanism underlying these associations. Purpose: This study investigated how specific dysfunctional family processes predict later smartphone addiction in Chinese adolescents and whether heterogeneous developmental trajectories of emotion-related impulsivity explain these relationships. Method: A sample of 1,434 Chinese adolescents (Mage = 12.64; SDage = 0.68 at Time 1; 56.8% boys) was assessed across four waves over two years, at six- to nine-month intervals. Dysfunctional family processes (physical/emotional abuse, physical/emotional neglect, interparental conflict, and paternal/maternal rejection) were measured at baseline. Emotion-related impulsivity was assessed at all four time points, and smartphone addiction was assessed at the final 2-year follow-up. Results: Latent class growth models revealed four latent classes of emotion-related impulsivity: high-stable (6.7%), high-decreasing (10.9%), low-increasing (24.4%), and low-stable (58.0%). Emotional abuse, interparental conflict, and paternal rejection were significant longitudinal predictors of smartphone addiction. These relationships were mediated by developmental trajectories of emotion-related impulsivity. Specifically, interparental conflict had indirect effects on smartphone addiction through membership in the high-stable, high-decreasing, and low-increasing groups of emotion-related impulsivity. Emotional neglect and paternal rejection had indirect effects via the high-stable group of emotion-related impulsivity, while emotional abuse was mediated by the high-decreasing group of emotion-related impulsivity. Conclusions: The findings demonstrate distinct pathways through which dysfunctional family processes contribute to smartphone addiction via impaired impulse control, highlighting interparental conflict as a particularly potent risk factor. These results underscore the critical need for intervention programs that target impulse regulation skills, particularly for adolescents exposed to familial adversity.