In 1919 a pioneering generation of scholars, social policy experts, and politicians designed an unprecedented international organizational framework for labour politics. The majority of the founding fathers of this new institution, the International Labour Organization (ILO), had made great strides in social thought and action before 1919. The core members all knew one another from earlier private professional and ideological networks, where they exchanged knowledge, experiences, and ideas on social policy. In this study, one key question is the extent to which prewar “epistemic communities”, such as the International Association for Labour Legislation (IALL), and political networks, such as the Second International, were a decisive factor in the institutionalization of international labour politics. In the postwar euphoria, the idea of a “makeable society” was an important catalyst behind the social engineering of the ILO architects. As a new discipline, international labour law became a useful instrument for putting social reforms into practice. This article also deals with how the utopian idea(l)s of the founding fathers – social justice and the right to decent work – were changed by diplomatic and political compromises made at the Paris Peace Conference. The article thus reflects the dual relationship between idealism and pragmatism.