A growing body of research shows that coalitions can be a crucial force in securing developmental reform. Coalitions of women are particularly important because they utilize collective power and resources to strengthen a group which is often politically marginalised. This paper is a case study of the gendered challenges and opportunities encountered by Tonga’s ‘Women in Leadership’ Coalition (WILC) in their advocacy for the ratification of CEDAW (Convention on the Elimination of all Forms of Discrimination Against Women), one of only seven remaining states which has not signed the convention. In addition to identifying key challenges and opportunities encountered by the coalition, we consider what was specifically gendered about these factors. Our primary data source is 26 elite interviews conducted with members of the coalition and a variety of stakeholders, including members of the government, civil service and religious leaders. We show how the historical evolution of member organisations from the Tongan women’s civil society sector has indeed presented the coalition with both gendered challenges and opportunities. Regarding local power dynamics, interests and incentives, we identify gendered relationships between coalition members, current and former governments, local religious leader and media. We conclude by making recommendations regarding how women’s coalitions can continue to build their capacity and links with stakeholders, and how donor organisations can help support these aims.