The current guidelines recommend that people consume 2 or more servings of fat-rich fish per week to obtain enough omega-3 (ω-3) polyunsaturated fatty acids to prevent cardiovascular events. However, the cardiovascular benefits of ω-3 polyunsaturated fatty acids in patients with diabetes are unclear, and related large-scale trials have produced conflicting results. We aimed to perform a meta-analysis of all randomized controlled trials that attempted to assess the effects of ω-3 fatty acid supplementation on cardiovascular outcomes in patients with diabetes. In PubMed, EMBASE, and the Cochrane Library, we searched for data from all randomized controlled trials on ω-3 fatty acids and cardiovascular outcomes in patients with diabetes published before July 2022. Eight eligible studies involving 57,754 participants were ultimately included. Meta-analysis showed that ω-3 fatty acid supplementation reduces cardiovascular disease (CVD) risk in patients with diabetes (rate ration [RR] = 0.93; 95% confidence interval [CI]: 0.90, 0.97;P= 0.0009). Among them, eicosapentaenoic acid (EPA), but not EPA plus docosahexaenoic acid (DHA), significantly reduced the risk of CVD in patients with diabetes (EPA [RR = 0.81; 95% CI: 0.73, 0.90;P=0.0001]). This meta-analysis suggests that ω-3 fatty acid supplementation is an effective strategy to prevent CVD in patients with diabetes, but further well-designed, large-scale randomized controlled trials are necessary to evaluate the safety of ω-3 fatty acid supplementation, and its effect on atrial fibrillation. This study was registered with PROSPERO as CRD42022346302.