Background: Anastomotic leak (AL) is a serious complication after gastrectomy. It is associated with prolonged hospital stay, greater expenses, and increased risk for 90-day mortality. Currently, there is no consensus regarding the effect of AL on OS in patients with GC undergoing gastrectomy. This study was designed to investigate the effect of AL on long-term survival after gastrectomy for gastric cancer. Methods: PubMed, Embase, Scopus, Google Scholar, and Cochrane Library were queried during the search process. The literature search started in January 2025 and was updated in May 2025. The studies analyzed the impact of AL on long-term survival, with the primary outcome being long-term overall survival. Pooled effect size measures included restricted mean survival time difference (RMSTD), hazard ratio (HR), and 95% confidence intervals (CIs). Results: Ten studies (11,862 patients) were included. Overall, 338 (2.9%) patients experienced AL. The RMSTD analysis indicates that at 12, 24, 36, 48, and 60 months, patients with AL tend to live 1.1, 3.1, 5.2, 8.1, and 10.6 months shorter, respectively, compared to those who did not develop AL. All results were statistically significant with p < 0.0001. The time-dependent HRs analysis for AL versus no AL shows a higher mortality hazard in patients with AL at 12 (HR 1.32, 95% CI 1.11–1.58), 24 (HR 1.61, 95% CI 1.34–1.92), 36 (HR 1.55, 95% CI 1.27–1.91), 48 months (HR 1.22, 95% CI 1.02–1.53), and 60 months (HR 0.79, 95% CI 0.59–1.10). Conclusions: This research appears to indicate a clinical impact of AL on long-term OS after gastrectomy. Patients experiencing AL appear to have an increased risk of mortality within the initial four years of follow-up.