Background Bipolar disorder is a source of marked disability, morbidity and premature death. There is a paucity of research on personalised psychosocial interventions for bipolar disorder, especially in low-resource settings. A pilot randomised controlled trial (RCT) of a culturally adapted psychoeducation intervention for bipolar disorder (CaPE) in Pakistan reported higher patient satisfaction, enhanced medication adherence, knowledge and attitudes regarding bipolar disorder, and improvement in mood symptom scores and health-related quality of life measures compared with treatment as usual (TAU). Aims The current protocol describes a larger multicentre RCT to confirm the clinical and cost-effectiveness of CaPE in Pakistan. Trial registration: NCT05223959. Method A multicentre individual, parallel-arm RCT of CaPE in 300 Pakistani adults with bipolar disorder. Participants over the age of 18, with a diagnosis of bipolar I or II disorder who are currently euthymic, will be recruited from seven sites: Karachi, Lahore, Multan, Rawalpindi, Peshawar, Hyderabad and Quetta. Time to recurrence will be the primary outcome assessed using the Longitudinal Interval Follow-up Evaluation (LIFE). Secondary measures will include mood symptoms, quality of life and functioning, adherence to psychotropic medications, and knowledge and attitudes regarding bipolar disorder. Results This trial will assess the effectiveness of the CaPE intervention compared with TAU in reducing the time to recurrence for people with bipolar disorder currently in remission in Pakistan and determine the effect on clinical outcomes, quality of life and functioning. Conclusions A successful trial might lead to rapid implementation of CaPE in clinical practice, not only in Pakistan, but also in other low-resource settings, including those in high-income countries, to improve clinical outcomes, social and occupational functioning, and quality of life in South Asian and other minority group patients with bipolar disorder.