The Belgian king Leopold II’s Independent Congo State is perhaps the best-known and most extreme example of the horrific impact that formal European colonization had upon Africans. Yet international advocacy on behalf of Congo’s people focused on atrocity and depopulation, not the state’s violation of their intrinsic rights as human beings. This essay seeks to identify the significance of the Congo reform movement for the history of human rights. It analyzes the process by which British consul Roger D. Casement sought to document and construct a case that would convince his government to use its influence to force a sovereign power to address the plight of the indigenous people in the king’s prized colony. The focus leads to a new analytical approach that identifies human rights advocacy as a practice of persuasion. Such a practice relies on careful evidence gathering, is informed by a sophisticated understanding of how prevailing norms and rights can be used to relieve suffering, and aims to convince a powerful intervener that action is both justified and possible.