This article asks why sexual orientation was included in the anti‐discrimination clause of the Treaty of Amsterdam (Article 13) in the absence of active support within the Council of Ministers and even though few Member States had established it as protected ground prior to the intergovernmental conference. A detailed historical analysis reveals how the European Parliament (EP) gradually developed into the hub of a transnational advocacy network that promoted gay rights to the European Commission and the Council. The dynamics of the intergovernmental conference enabled the EP to introduce sexual orientation into the treaty‐making process, while the use of naming‐and‐shaming tactics vis‐à‐vis the Dutch Presidency secured the ground's final inclusion. This political history has theoretical implications since it presents a challenge to extant liberal intergovernmentalist and institutionalist analyses of the Amsterdam Treaty and suggests that the EP should be afforded more attention by neofunctionalist scholars.