South Asian adults in the US experience excess cardiovascular disease (CVD) compared with other racial and ethnic groups. The effectiveness and reach of guideline-recommended lifestyle interventions have not been evaluated in this population. To evaluate whether a culturally adapted, group lifestyle intervention will improve CVD risk factors more effectively than written health education materials among US South Asian adults. This single-blind randomized clinical trial was conducted from March 6, 2018, to February 11, 2023 at community sites in the Chicago, Illinois, metropolitan area. South Asian adults aged 18 to 65 years who were overweight or obese, had no history of CVD events, and had at least 1 additional CVD risk factor (hypertension, dyslipidemia, prediabetes, or diabetes) were eligible for inclusion. A 16-week, culturally adapted, group-based lifestyle intervention led by community health coaches. Lifestyle modification counseling was delivered in English, Gujarati, Hindi, and Urdu. Participants tracked their diet and physical activity (PA) and received 4 optional group maintenance sessions between months 5 and 11 of follow-up. The intervention was delivered in person prior to the onset of the COVID-19 pandemic and via videoconference starting in March 2020. The control group received written health education materials, delivered monthly. Primary outcomes were the between-group differences in CVD risk factor changes from baseline to 12 months, including weight, systolic blood pressure (SBP), diastolic blood pressure (DBP), glycated hemoglobin (HbA1c), and total cholesterol, estimated using multivariate mixed-effects regression models. Secondary outcomes were self-reported diet quality, PA, and self-efficacy, estimated using univariate mixed-effects regression models. Among 549 randomized participants, 318 (57.9%) were women, and mean (SD) participant age was 49.2 (9.5) years. Mean differences in CVD risk factor changes from baseline to 12 months in the intervention vs control group were calculated for weight (mean difference, -0.07 kg; 95% CI, -0.55 to 0.42), SBP (mean difference, 0.47 mm Hg; 95% CI, -1.85 to 2.79), DBP (mean difference, 0.44 mm Hg; 95% CI, -1.06 to 1.95), cholesterol (mean difference, -2.47 mg/dL; 95% CI, -8.51 to 3.57), and HbA1c (mean difference, -0.07%; 95% CI -0.20% to 0.07%). Intervention participation was associated with greater improvements in dietary quality, PA, and self-efficacy than control. In the SAHELI randomized clinical trial, a culturally adapted, group lifestyle intervention was not more effective than written health education materials for CVD risk factor reduction among US South Asian adults, but the intervention was associated with small improvements in self-reported health behaviors. Effective CVD prevention interventions for this elevated-risk population require further investigation. ClinicalTrials.gov Identifier: NCT03336255.