Over the past decade, international non-governmental organizations (NGOs) have been contesting the neo-liberal economic order in international politics by campaigning for normative conditions to bring about what Richard Falk calls 'humane governance'. However, the degree to which NGOs have contributed to the formation of global social contracts remains controversial. While NGO activists and various scholars advocate the establishment of such contracts, empirical testing of this normative argument is underdeveloped. Drawing upon this lack of empirical support, critics dismiss the global social contract concept and question the roles played by NGOs in international politics. This article addresses the controversy through a review, refinement and application of global social contract theory and an empirical study of two prominent international NGO campaigns directed at the World Trade Organization (WTO), an institution that represents a 'hard test case'. It explores the ways in which NGOs and their networks are challenging the neo-liberal basis of WTO agreements and contributing to the emergence of global social contracts. The article concludes that in some circumstances, NGOs have the capacity to inject social justice into international economic contracts and there is some basis for optimism regarding the formation of global social contracts involving NGOs, nation-states and international organizations.