Background: Recent advances in the treatment of Gastric Cancer (GC) have introduced immunotherapy as a promising approach for advanced disease. In this context, potential biomarkers such as the platelet-to-lymphocyte ratio (PLR) and neutrophil-to-lymphocyte ratio (NLR) have gained attention for their roles in predicting treatment outcomes. In this meta-analysis, we explore the clinical significance of PLR and NLR as predictors of Overall Survival (OS) and Progression-Free Survival (PFS) in advanced GC patients undergoing immunotherapy. Methods: Two independent reviewers systematically searched electronic databases, including PubMed, Embase and Scopus. The search incorporated controlled vocabulary (MeSH terms) and keywords related to Gastric Cancer, immunotherapy, platelet-to-lymphocyte ratio (PLR), and neutrophil-to-lymphocyte ratio (NLR). Eligible studies were selected based on predefined criteria, including HR availability, and were assessed for quality and bias using the Newcastle-Ottawa Scale. Data extraction was independently performed by two reviewers, and discrepancies in study selection and data extraction were resolved by a third reviewer. Subgroup analyses were performed to explore potential variations in the study outcomes. All analyses were conducted with RevMan 5.4 and employed random-effects model. Results: In total, 16 studies encompassing 1176 patients for NLR and 8 studies covering 766 patients for PLR were included in this systematic review and meta-analysis. The studies spanned the years between 2018 and 2023. Our analysis revealed significant associations between high NLR and poor OS (HR: 2.11, 95% CI: 1.70-2.62, p < 0.00001) and PFS (HR: 1.76, 95% CI: 1.43-2.17, p < 0.00001). Similarly, elevated PLR was significantly associated with worse OS (HR: 1.77, 95% CI: 1.44-2.17, p < 0.00001) and PFS (HR: 1.61, 95% CI: 1.33-1.96, p < 0.00001). In all conducted subgroup analyses, high NLR and PLR were consistently associated with poor survival outcomes. Conclusions: Our analysis supports the significance of NLR and PLR as accessible and cost-effective biomarkers for predicting survival outcomes in the context of immunotherapy for advanced GC. These findings underscore their potential significance in guiding clinical decisions. Further investigation should be carried out to validate our findings.