Complete revascularization (CR) in patients with acute coronary syndromes (ACS) and multivessel disease (MVD) improves clinical outcomes compared with culprit-only revascularization, but the optimal timing for non–culprit lesions treatment remains unclear. This study evaluated patients presenting with ACS and MVD admitted between January 2015 and September 2021 at the Erasmus University Medical Center. Clinical outcomes were compared between immediate and staged CR in terms of major adverse cardiac and cerebrovascular events (MACCEs), a composite of all-cause mortality, myocardial infarction, stroke, and any unplanned revascularization. A total of 1,400 patients presenting with ACS and MVD who underwent immediate or staged CR were included in this study. Using 1/many propensity score matching without replacement, 299 patients in the staged CR group were matched to 598 patients in the immediate CR group (mean 1:2 ratio), rendering a total of 897 patients for analysis. The median follow-up period was 648 days. MACCE rate was significantly higher in the staged CR group than in the immediate CR group (adjusted hazard ratio [95% confidence interval] 1.60 [1.05 to 2.45], p = 0.03). Furthermore, number of stents, stent length, and contrast usage were significantly greater in the staged revascularization group. Immediate CR was associated with less risk of MACCE than was staged CR. Staged CR required overall more contrast and stent material.