Sovereignty and human rights are generally considered separate, mutually contradictory regimes in international society. This article takes issue with this conventional assumption, and argues that only by treating sovereignty and human rights as two normative elements of a single, inherently contradictory modern discourse about legitimate statehood and rightful state action can we explain key moments in the expansion of the international system during the twentieth century. After developing a constructivist argument about communicative action, norm formation and sovereignty, the article focuses on post-1945 decolonization, showing how ‘first wave’ post-colonial states played a crucial role in constructing the ‘international bill of rights’, how they invoked those rights to justify the norm of self-determination, and how this norm in turn licensed the proliferation of new sovereign states in Asia and elsewhere.