ABSTRACT In the literature exploring the associations between problematic social media use (SMU) and sleep, the majority of studies focus on problematic SMU as a predictor of poorer sleep outcomes. There is currently a scarcity of empirical investigation of the reverse causal direction. Therefore, the aim of this study was to investigate the impact of sleep (insomnia and sleep quality) on problematic social media use and the mediating role of motives for SMU. The eMediate study participants (young adult social media users from Bangladesh) who completed four surveys of SMU, sleep, and mental health at three‐month intervals were included ( n = 426, 49.8% female, mean age = 22.61 ± 1.83 years). Multilevel mediation analyses were conducted to examine the impact of sleep problems on problematic social media use through motives for SMU. Sleep problems significantly predicted SMU for coping, conforming, escapism, social support seeking, and decreasing negative emotions motives, as well as problematic social media use . Motives mediated 41% of the effect of insomnia symptoms and 71% of the effect of poor sleep quality on problematic social media use . SMU for coping and escapism motives mediated the associations between sleep problems and subsequent problematic social media use . SMU for coping with sleep problems and escaping from associated worries arising from sleep problems and real‐life difficulties may reinforce use by providing short‐term relief and leading to reliance on SMU.