Science plays an important role in the emergence, development, and implementation of new environmental regimes. However, there are opposing views regarding the type of knowledge that is considered policy-relevant to address global environmental problems. In intergovernmental negotiations, these tensions are visible in debates about the inclusion of scientific concepts in a negotiated text. This article analyses the case of “ecological connectivity” in the negotiations for an international legally-binding instrument (ILBI) for the conservation and sustainable use of marine biodiversity of areas beyond national jurisdiction (BBNJ). As a key scientific concept portraying the ocean as one, the term ecological connectivity challenges the status quo and has far-reaching implications for future ocean governance. Our study draws on ethnographic data collected during the BBNJ negotiations and analyses the actors and their different rationales for including the ecological connectivity concept in the treaty text. Our results demonstrate two things. First, state and non-state actors use the ecological connectivity concept to support their interests in the new ILBI, based on different types of rationales: ecologic, socio-economic, juridic, and epistemic. Second, our analysis demonstrates that several actors recognise the limitations of the existing legal order underpinning ocean governance in areas beyond national jurisdiction and are keen to embrace a new legal framework regarding the idea of an interconnected ocean. We conclude that while the ecological connectivity concept runs the risk of losing its meaning in an array of competing political interests, it does have the potential to achieve transformative change in global ocean governance and fundamentally alter the way humans use and protect BBNJ.