Background: The treatment gap for bipolar disorder is aggravated by economic inequality. Around half of the world's population live in a low-or lower-middle-income country, where research on treatment is scarce. Hence, this review aims to determine the number and types of intervention studies conducted on adults with bipolar disorder in low-income and lower-middle-income countries and analyze the effect of these interventions on symptom severity, medical adherence, and quality of life. Methods: A systematic review was conducted in June and November 2021 using eight databases. Controlled intervention trials on adults with bipolar disorder on data from low-income and lower-middle-income countries at time of publication were included. The risk of bias was assessed using the Revised Cochrane risk-of-bias tool for randomized trials or The Risk Of Bias In Non-randomized Studies of Interventions assessment tool. Results: Twenty-one studies met the inclusion criteria. These were divided into four subtypes based on the intervention; pharmacotherapy (=12), psychosocial (=7), electroconvulsive therapy (=1), and traditional medicine (=1). Three studies were from low-income countries. A high risk of bias characterized the studies; only four studies reported the procedures used for randomization. Most studies, however, identified a beneficial effect on symptom severity, and in addition, medical adherence could be improved with psychosocial interventions. Limitations: Heterogeneity across studies prevented any meaningful pooling of data to meta-analyses. Conclusion: Data for treatment interventions contextualized to the local setting for bipolar disorder remains sparse, particularly from low-resource settings. Further studies are urgently needed to target the treatment gap for bipolar disorder. Trial registration: PROSPERO: CRD42020170953.