BACKGROUND: Tobacco smoking is common in people living with HIV, but high-quality evidence on interventions for smoking cessation is not available in this population. We aimed to assess the efficacy and safety of varenicline with counselling to aid smoking cessation in people living with HIV. METHODS: The ANRS 144 Inter-ACTIV randomised, parallel, double-blind, multicentre, placebo-controlled phase 3 trial was done at 30 clinical hospital sites in France. People living with HIV who had smoked at least ten cigarettes per day for 1 year or longer, were motivated to stop smoking, were not dependent on another psychoactive substance, and had no history of depression or suicide attempt were eligible. Using a computer-generated randomisation sequence, we allocated (1:1) the patients to receive either varenicline titrated to two 0·5 mg doses twice daily or placebo twice daily for 12 weeks, plus face-to-face counselling. Patients and investigators were masked to treatment group allocation. Patients who were not abstinent at week 24 were offered open-label varenicline for 12 additional weeks. The primary outcome was the proportion of smokers continuously abstinent from week 9 to week 48. Smoking status was confirmed by carbon monoxide in exhaled air. Primary analyses were done in both the intention-to-treat (ITT) population and modified ITT (mITT) population, which comprised all patients who took at least one tablet of their assigned study treatment. The safety analyses were done in the mITT population. The trial is registered at ClinicalTrials.gov, number NCT00918307. The trial status is complete. FINDINGS: From Oct 26, 2009, to Dec 20, 2012, of 303 patients assessed for eligibility, 248 patients were randomly assigned to the varenicline group (n=123) or the placebo group (n=125). After randomisation, one participant initially assigned to the placebo group was excluded from the ITT analysis for a regulatory reason (no French health-care coverage). 102 patients in the varenicline group and 111 patients in the placebo group received at least one dose of their assigned treatment and were included in the mITT analysis. In the ITT analysis, varenicline was associated with a higher proportion of patients achieving continuous abstinence over the study period (week 9-48): 18 (15%, 95% CI 8-21) of 123 in the varenicline group versus eight (6%, 2-11) of 124 in the placebo group, adjusted odds ratio (OR) 2·5 (95% CI 1·0-6·1; p=0·041). In the mITT analysis, varenicline was also associated with higher continuous abstinence: 18 (18%, 95% CI 10-25) of 102 versus eight (7%, 2-12) of 111 in the placebo group (adjusted OR 2·7, 95% CI 1·1-6·5; p=0·029). The incidence of depression was 2·4 per 100 person-years (95% CI 0·6-9·5; two [2%] of 102) in the varenicline group and 12·4 per 100 person-years (95% CI 6·9-22·5; 11 [10%] of 111) in the placebo group. 14 (7%) of 213 participants had 18 cardiovascular events: six (6%) of 102 people in the varenicline group and eight (7%) of 111 people in the placebo group. INTERPRETATION: Varenicline is safe and efficacious for smoking cessation in people living with HIV and should be recommended as the standard of care. FUNDING: The French National Institute for Health and Medical Research (INSERM)-French National Agency for Research on AIDS and Viral Hepatitis (ANRS) and Pfizer.