Environmental conditionality is increasingly considered as part of the Free Trade Agreements (FTA) in the European Union (EU) as part of its wider efforts towards sustainable development and the development of the blue economy. The following paper critically looks at the legal design, enforceability, and practical implications of such conditionality with specific reference to fisheries partnership agreements, sustainability chapters in new EU FTAs, and how the nexus between trade liberalization and marine environmental protection is changing. Although environmental conditionality shows the effort of the EU to externalize its goals of the Green Deal and biodiversity, its engagement with the international trade law, especially the World Trade Organization (WTO) disciplines, triggers complex issues of non-discrimination, proportionality, and extraterritoriality. In a comparative review of the latest agreements, the article evaluates whether environmental conditionality is an effective governance instrument to protect marine ecosystems, fight illegal, unreported, and unregulated (IUU) fishing, and promote sustainable blue economy practices. It further reflects the issues of monitoring and dispute settlement, as well as the low enforceability of the sustainability provisions. The article maintains that, unless entrenched within a transnational legal framework, which is coherent (in the sense of uniting obligations under the United Nations Convention on the Laws of the Sea (UNCLOS), the jurisprudence of WTO and EU governance systems) environmental conditionality may continue to be a marginal tool. The article ends by suggesting ways in which conditionality could be further bolstered by specifying conditions, further benchmarks, hybrid forms of enforcement, as well as consistency with the duties to conduct due diligence in the creation of global ocean governance of corporations in the EU.