Background and Objectives: The triglyceride–glucose (TyG) index is an accessible surrogate marker of insulin resistance and has been increasingly investigated for its prognostic relevance in cardiovascular disease. However, evidence regarding its predictive value for major adverse cardiovascular events (MACEs) in patients with acute coronary syndromes (ACSs) remains inconsistent. This study systematically assessed the association between TyG index and the risk of MACEs in individuals with ACS. Materials and Methods: Following PRISMA 2020 guidelines, PubMed, ScienceDirect, and ClinicalTrials.gov were searched through October 2025. Ten observational cohort studies including 32,751 ACS patients were analyzed. Studies reporting fully adjusted hazard ratios (HRs) for the association between TyG index and MACEs were eligible. A random-effects model was used to pool effect sizes expressed as adjusted HRs per 1-unit increase in the TyG index. Heterogeneity, sensitivity analyses, publication bias assessment, and meta-regression were conducted. Results: Higher TyG index values were significantly associated with increased MACE risk (pooled adjusted HR 1.45, 95% CI 1.25–1.68, I² = 80%). Leave-one-out analysis confirmed robustness. Meta-regression analysis suggested a stronger association in cohorts consisting exclusively of patients with type 2 diabetes mellitus, with a trend toward larger effect estimates in smaller studies, potentially contributing to the observed heterogeneity. Despite small-study effects, trim-and-fill-adjusted estimates remained significant (HR 1.26, 95% CI 1.05–1.52). Conclusions: An elevated TyG index is independently associated with higher MACE risk in ACS patients and may be considered as an additive metabolic risk marker in combination with established risk stratification tools, pending further prospective validation.