Marine tailings disposal, including Deep Sea Tailings Placement (DSTP) and shallow-water submarine tailings disposal, is used as an alternative to land-based tailings storage where onshore options are constrained by climate, topography, land availability, biodiversity, or social impacts. For some critical minerals’ projects, DSTP is considered a technically feasible option. However, DSTP is increasingly contested by regulators, investors, non-government organisations, communities, and downstream supply chains due to uncertainties about deep-sea ecosystems, long-term impacts and the difficulty of monitoring and remediation once waste is placed on the sea floor. This paper synthesises recent international experience from current and proposed DSTP operations in Papua New Guinea, Indonesia, Turkey and Norway, alongside global policy developments such as the London Protocol, regional guidance in the Pacific and the European Union’s Best Available Techniques reference documents, and the 2016 International Union for Conservation of Nature (IUCN) resolution calling for an end to sea disposal of extractive waste. It examines how lender, industry, and supply chain standards (including International Finance Corporation / World Bank Group (IFC/WBG), International Council on Mining and Metals (ICMM), Global Industry Standard on Tailings Management (GISTM), Mining Association of Canada / Towards Sustainable Mining (MAC/TSM), Initiative for Responsible Mining Assurance (IRMA), the Copper Mark, the World Gold Council, and the Responsible Jewellery Council) are reshaping the acceptability and financing of marine tailings disposal. The analysis highlights rising legal, environmental, social, and reputational risks for new DSTP projects, including litigation, permitting challenges, community opposition, and potential constraints on access to capital and premium markets. In response, the paper proposes a practical framework for DSTP built around eight pillars: alignment with good international industry practice, structured stakeholder engagement, rigorous comparative environmental and social impact assessment of all tailings options, robust environmental and social management planning, comprehensive monitoring and reporting, clear closure and post-closure strategies, independent expert review and regulatory compliance. The paper concludes that marine tailings disposal should only be used where it demonstrably presents a lower overall risk profile than terrestrial alternatives and is implemented with high levels of transparency and accountability.