This article deploys a historical analysis of the relationship between law and imperialism to highlight questions about the character and role of international law in global politics. The involvement of two British international lawyers in practices of imperialism in Africa during the late nineteenth century is critically examined: the role of Travers Twiss (1809–1897) in the creation of the Congo Free State and John Westlake’s (1828–1913) support for the South African War. The analysis demonstrates the inescapably political character of international law and the dangers that follow from fusing a particular form of liberal moralism with notions of legal hierarchy. The historical cases raise ethico-political questions, the importance of which is only heightened by the character of contemporary world politics and the attention accorded to international law in recent years.