BACKGROUND: The workplace offers a unique opportunity for effective health promotion. We aimed to comprehensively study the effectiveness of multicomponent worksite wellness programmes for improving diet and cardiometabolic risk factors. METHODS: We did a systematic literature review and meta-analysis, following PRISMA guidelines. We searched PubMed-MEDLINE, Embase, the Cochrane Library, Web of Science, and Education Resources Information Center, from Jan 1, 1990, to June 30, 2020, for studies with controlled evaluation designs that assessed multicomponent workplace wellness programmes. Investigators independently appraised the evidence and extracted the data. Outcomes were dietary factors, anthropometric measures, and cardiometabolic risk factors. Pooled effects were calculated by inverse-variance random-effects meta-analysis. Potential sources of heterogeneity and study biases were evaluated. FINDINGS: From 10 169 abstracts reviewed, 121 studies (82 [68%] randomised controlled trials and 39 [32%] quasi-experimental interventions) met the eligibility criteria. Most studies were done in North America (57 [47%]), and Europe, Australia, or New Zealand (36 [30%]). The median number of participants was 413·0 (IQR 124·0-904·0), and median duration of intervention was 9·0 months (4·5-18·0). Workplace wellness programmes improved fruit and vegetable consumption (0·27 servings per day [95% CI 0·16 to 0·37]), fruit consumption (0·20 servings per day [0·11 to 0·28]), body-mass index (-0·22 kg/m2 [-0·28 to -0·17]), waist circumference (-1·47 cm [-1·96 to -0·98]), systolic blood pressure (-2·03 mm Hg [-3·16 to -0·89]), and LDL cholesterol (-5·18 mg/dL [-7·83 to -2·53]), and to a lesser extent improved total fat intake (-1·18% of daily energy intake [-1·78 to -0·58]), saturated fat intake (-0·70% of daily energy [-1·22 to -0·18]), bodyweight (-0·92 kg [-1·11 to -0·72]), diastolic blood pressure (-1·11 mm Hg [-1·78 to -0·44]), fasting blood glucose (-1·81 mg/dL [-3·33 to -0·28]), HDL cholesterol (1·11 mg/dL [0·48 to 1·74]), and triglycerides (-5·38 mg/dL [-9·18 to -1·59]). No significant benefits were observed for intake of vegetables (0·03 servings per day [95% CI -0·04 to 0·10]), fibre (0·26 g per day [-0·15 to 0·67]), polyunsaturated fat (-0·23% of daily energy [-0·59 to 0·13]), or for body fat (-0·80% [-1·80 to 0·21]), waist-to-hip ratio (-0·00 ratio [-0·01 to 0·00]), or lean mass (1·01 kg [-0·82 to 2·83]). Heterogeneity values ranged from 46·9% to 91·5%. Between-study differences in outcomes were not significantly explained by study design, location, population, or similar factors in heterogeneity analyses. INTERPRETATION: Workplace wellness programmes are associated with improvements in specific dietary, anthropometric, and cardiometabolic risk indicators. The heterogeneity identified in study designs and results should be considered when using these programmes as strategies to improve cardiometabolic health. FUNDING: National Heart, Lung, and Blood Institute.