Sleep abnormalities are core features of bipolar disorders (BD), but they have not been thoroughly examined across mood phases. This meta-analysis investigated sleep disturbance prevalence and sleep characteristics differences in BD across mood phases. A systematic search through September 2024 identified 44 studies (7614 BD cases, 3164 controls), including 11 prevalence and 34 case-control studies. Poor sleep quality prevalence was 52% during euthymia, and insomnia prevalence was 63% during the depressive phase. Individuals with euthymic BD reported worse sleep quality and objectively measured longer total sleep time and sleep onset latency than controls. Depressive phase BD showed higher rapid eye movement percentages, while manic/mixed phase exhibited shorter total sleep time, lower sleep efficiency, and longer sleep onset latency. During euthymia, BD demonstrated greater variability in sleep duration and continuity, and more prominent sleep differences when assessed with sleep diary versus objective sleep measures, highlighting the importance of integrating objective assessments and patient-reported outcomes. Overall, these findings indicate that poor sleep quality and insomnia are highly prevalent in BD, and that some sleep parameter differences are present during euthymia, while others occur during depressive and manic phases, emphasizing the need for sleep assessments and tailored management throughout the course of BD.