In this paper I propose a novel account of international law as a subset of international political argument, in turn understood as a practice of deliberative discourse. I draw on a Habermasian communicative framework to integrate legal and political argument, facilitating a more nuanced and more plausible understanding of how international law and politics interact. Through a detailed examination of two historical cases from the first decade of the Northern Ireland conflict, involving the United Nations and the European Convention on Human Rights respectively, I illustrate three key dimensions of this framework: the relation between legal and political argument; the relation between domestic and international argument; and the distinction between strategic and communicative uses of legal argument.