In an increasingly data‑driven marketplace, firms are investing heavily in Decision Support Systems to guide strategic marketing decisions, yet the pathways through which such systems contribute to sustainable competitive advantage remain inadequately understood. This study addresses this gap by examining the direct, mediated, and moderated effects of DSS leverage on competitive advantage. Specifically, it tests whether strategic marketing decision quality mediates the DSS‑advantage relationship and whether market dynamism moderates the impact of DSS on decision effectiveness. A quantitative, cross‑sectional survey was conducted with 280 marketing managers, strategic planners, and senior executives from medium‑to‑large enterprises across manufacturing, services, and technology sectors. Data were analysed using Partial Least Squares Structural Equation Modelling with 5,000 bootstrap samples. The results fully support all three hypotheses. DSS leverage has a significant direct positive effect on sustainable competitive advantage (β = 0.42, p < 0.001). Strategic marketing decision quality partially mediates this relationship, accounting for 60% of the total effect. Furthermore, market dynamism positively moderates the DSS‑decision quality link (β = 0.31, p < 0.001), with the impact of DSS being substantially stronger in highly dynamic environments. Control variables (firm size, industry type, marketing budget) were non‑significant. The study concludes that DSS not only directly enhances competitive advantage but also does so indirectly by improving strategic decision quality, and that this indirect effect is amplified under conditions of rapid market change. These findings offer actionable guidance for marketing leaders regarding DSS investment, integration into decision processes, and calibration according to environmental turbulence. Theoretical contributions include integrating the resource‑based view with dynamic capabilities theory in a tested moderated‑mediation model.