Background/Objectives: SNMM is a rare and aggressive malignancy with a poor prognosis. The current staging systems fail to adequately stratify patient risk. This study aimed to evaluate the prognostic impact of tumor location and extension on overall survival (OS) in SNMM. Methods: A systematic literature search of Medline, Web of Science, and Embase was performed to identify studies assessing the prognostic significance of tumor location and extension. Study quality was evaluated using the Quality in Prognosis Studies (QUIPS-2) tool. Meta-analyses were conducted to calculate pooled hazard ratios (HRs) with 95% confidence intervals (CIs). Eligible studies included primary SNMM reporting tumor location/extension and survival; observational designs (case series ≥ 5 patients) were eligible with no language restrictions. Searches covered MEDLINE, Web of Science, and Embase and were last updated on 10 Jan 2025; reference lists were also screened. Results: Thirty-four studies were included in the systematic review, of which ten met criteria for meta-analysis. Tumors located in the paranasal sinuses (HR = 2.89, 95% CI: 1.63–5.14) and those with orbital involvement (HR = 1.92, 95% CI: 1.34–2.73) were associated with significantly poorer OS. Maxillary and ethmoid sinus involvement showed no statistically significant difference compared with nasal cavity tumors. Conclusions: Tumor location and extension are significant prognostic indicators in SNMM. Patients with paranasal sinus tumors or orbital invasion have worse outcomes, supporting inclusion of these factors in future staging systems for better clinical decision-making. Limitations include the observational nature of the evidence, heterogeneity across definitions and analyses, and underpowered publication-bias tests; certainty of evidence was not formally graded.