The governance of marine biodiversity in areas beyond national jurisdiction (BBNJ) lacks a legal framework that would ensure the conservation and sustainable use of the oceans. In order to fill this gap, governments have been negotiating a new treaty under the United Nations Convention on the Law of the Sea. Negotiations have been afflicted by polarisation between two principles: The ‘Freedom of the High Seas’ (FOS) and the ‘Common Heritage of Humankind’ (CHP). Instead of discussing the CHP from a purely legal perspective, we examined, through an ethnographic lens, how it has become a practice of contestation: it is used as a tool and negotiation technique to challenge deeply rooted inequalities in the current world order. The CHP could make a difference if it was integrated into the text as a general principle committing all states to protect and preserve BBNJ for future generations – regardless of their imminent economic value as commercial assets.