The topic of women and girls’ rights, access and inclusion in sport and physical activity has become a mainstay of sporting and non-sporting organisational discourse. Notwithstanding, there is little published on why, how and who enabled these topics to become politicised to this extent. For example, academic texts state key moments for the advancement of women and sport, such as conferences and resolutions, but rarely provide further detail. By explaining how transnational women and sport advocacy groups lobbied the United Nations (UN) and the International Olympic Committee (IOC) into actions for women and sport in the mid-1990s, this article adds to knowledge about how advocacy groups in international sport succeeded in working together to collectively effect change despite demonstrating contention amongst one another. Data from archival analysis of papers and correspondence of key agents involved in these processes were complemented with semi-structured interviews with some of the same individuals decades later. Using terms and concepts from social movement studies, the article shows how the International Working Group on Women and Sport (IWG) and WomenSport International (WSI) developed in relation to each other and the political environment in which they were playing a key role in shaping. Their relationship was not straightforward, due in part to the formations and structure of each group, but their purposive efforts with other agents contributed to a collective endeavour that achieved milestones for the political legitimacy of women and sport.