IntroductionHeavy alcohol use among people living with HIV in sub-Saharan Africa can hinder the success of HIV treatment programmes, impacting progress towards United Nations Programme on HIV/AIDS goals. Primary partners can provide critical forms of social support to reduce heavy drinking and could be included in motivational interviewing (MI) interventions to address heavy drinking; however, few studies have evaluated MI interventions for couples living with HIV in sub-Saharan Africa. We aim to evaluate the feasibility and acceptability of a couple-based MI intervention with mobile breathalyser technology to reduce heavy alcohol use and improve HIV treatment outcomes among HIV-affected couples in South Africa.Methods and analysisWe will employ a three-arm randomised controlled trial to assess the efficacy of couple-based MI (MI-only arm) and in conjunction with mobile breathalysers (MI-plus arm) to address alcohol use and HIV outcomes, as compared with enhanced usual care (control arm). We will enrol heterosexual couples aged 18–49 in a primary relationship for at least 6 months who have at least one partner reporting hazardous alcohol use and on antiretroviral therapy for 6 months. Participants in both MI arms will attend three manualised counselling sessions and those in the MI-plus arm will receive real-time feedback on blood alcohol concentration levels using a mobile breathalyser. Couples randomised in the control arm will receive enhanced usual care based on the South African ART Clinical Guidelines. Feasibility and acceptability indicators will be analysed descriptively, and exploratory hypotheses will be examined through regression models considering time points and treatment arms.Ethics and disseminationThe study was approved by the University of California, San Francisco (HRPP; protocol number 21-35034) and Human Sciences Research Council Research Ethics Committee (REC: protocol number 1/27/20/21). We will disseminate the results at local community meetings, community-level health gatherings and conferences focused on HIV and alcohol use.Trial registration numberISRCTN05756790.