The COVID-19 pandemic has significantly increased the use of online tools in the conduct of multilateral environmental negotiations. Although scholars have recognized that information and communication technologies have gradually been reshaping traditional diplomatic practice, such technologies are not considered to be transformative of diplomatic practice itself. However, owing to the COVID-19 pandemic states have had to rush into unprecedented and unpredictable forms of digital cooperation that are poorly understood. To illuminate this uncharted area, our research applies combined digital and critical policy ethnography to two online dialogues within the framework of ongoing negotiations under the United Nations Convention on the Law of the Sea toward a new treaty for the protection and sustainable use of marine biodiversity beyond national jurisdiction. Digital critical policy ethnography conducted at two online sites enables us to study the political effects of emerging international practices. We re-interpret digital diplomacy in terms of “communities of practice” developing across, and connecting physical and digital sites. Virtual communications amongst state and non-state actors mirror traditional forms of diplomacy whilst introducing new practices that may change conventional forms of international treaty-making. We propose the term digital multilateralism to capture these new forms and conclude that it can have two effects: deepen the background knowledge of actors that form a community of practice and create new inequalities.