In recent decades, marine pollution has evolved beyond a predominantly environmental concern to become an issue with significant geopolitical and security implications, owing to its interactions with shared resources, critical infrastructure, economic interests, and relations among coastal states. This study examines the mechanisms through which pressures arising from marine pollution may generate security and geopolitical implications for the Islamic Republic of Iran, focusing on two strategically important marine regions: the Caspian Sea and the Persian Gulf. The research adopts a qualitative, descriptive-analytical approach based on a systematic documentary analysis of scientific literature published between 2018 and 2026. The findings indicate that marine pollution does not automatically constitute a security threat. Rather, its consequences emerge from the interaction of environmental pressures, exposure and vulnerability, and the mediating effects of legal, institutional, and geopolitical factors. In the Persian Gulf, vulnerability is exacerbated by the concentration of energy and maritime infrastructure, the strategic importance of shipping and the Strait of Hormuz, water–energy interdependence, regional tensions, and the militarization of the maritime environment. In the Caspian Sea, by contrast, the transboundary nature of pollution, the ecological interdependence of coastal states, hydrological changes, and constraints on regional cooperation are particularly significant. The identified implications can be classified into four domains: human security, economic security, strategic security, and regional diplomacy and cooperation. Accordingly, in light of the Islamic Republic of Iran’s General Environmental Policies and national development plans, the study identifies several policy imperatives: strengthening marine environmental governance and integrated management, establishing continuous pollution-monitoring systems, expanding regional and transboundary cooperation, enhancing environmental diplomacy, and integrating environmental considerations into national security and development decision-making.