Background: Psychoeducation is a cornerstone as an add-on to pharmacotherapy in standard care for individuals with bipolar disorder. However, evidence of the effectiveness of psychoeducation in low-resource settings is scarce. Aims: We aimed to assess the effectiveness of structured group psychoeducation versus waiting list on relapse prevention for individuals with bipolar disorder in Rwanda, a low-income country. Methods: This was a randomized open-label superiority trial. Participants aged 18 years or older with bipolar disorder were recruited at the two referral hospitals for mental health in Rwanda and randomly assigned 12 sessions of group psychoeducation or a waiting list. The program was tailored to the setting and co-designed with patients and clinicians. The follow-up period was 12 months, and the primary outcome mean number of psychiatric hospitalizations. Results: In February and March 2021, 154 participants were randomly assigned to receive group psychoeducation (n = 78) or to a waiting list (n = 76). The retention rate was high, with only three discontinuing the psychoeducation once they had received a session. Despite limited use of first-line pharmacotherapy, the psychoeducation reduced the risk of hospitalization by half during the 12-month follow-up (RR: 0.50(95 % CI 0.26–0.95)). Yet, no change in medical adherence was observed. Limitation: Weekly assessment of clinical status was not feasible. Conclusion: Structured group psychoeducation for bipolar disorder in a low-resource setting has a protective effect against readmission despite limited access to first-line pharmacotherapy. Further studies are needed to assess the effectiveness of the program in more decentralized settings with less highly trained staff. Trial registration: NCT04671225