The benefit of complete revascularization (CR) in ST-segment elevation myocardial infarction (STEMI) patients with left ventricular (LV) dysfunction is uncertain. A total of 1314 STEMI patients with multivessel coronary artery disease were analyzed. CR was defined angiographically and by a residual Synergy between PCI with Taxus and Cardiac Surgery trial (SYNTAX) score (SS) <8. Patients with a left ventricular ejection fraction (LVEF) <40% were classified as the reduced LVEF group. The major study endpoints were patient-oriented composite outcome (POCO) and cardiac death during three-year follow-up. Overall, patients that received angiographic CR (579 patients, 44.1%) had significantly lower three-year clinical events compared with incomplete revascularization (iCR). CR reduced three-year POCO and cardiac death rates in the preserved LVEF group (POCO: 13.2% vs. 21.9%, p < 0.001, cardiac death: 1.8% vs. 6.5%, p < 0.001, respectively) but not in the reduced LVEF group (POCO: 26.0% vs. 33.1%, p = 0.275, cardiac death: 15.1% vs. 19.0%, p = 0.498, respectively). Multivariate analysis showed that CR significantly reduced three-year POCO (hazard ration (HR) 0.59, 95% confidence interval (CI) 0.43–0.82) and cardiac death (HR 0.34, 95% CI 0.14–0.80), only in the preserved LVEF group. Additionally, the results were corroborated using the SS-based CR definition. In STEMI patients with multivessel disease, CR did not improve clinical outcomes in those with reduced LVEF.