For the past century, the Women’s International League for Peace and Freedom (WILPF) has acted as a forum for women from across the political spectrum to come together in pursuit of international peace and political, economic, and social justice for all. A close examination of the political make-up of membership within the British branch of the WILPF and the mechanisms through which British women from different political backgrounds forged and sustained a working partnership with each other and their international sisters in the decades between the two world wars provides a valuable case study in women’s collaboration across ideological divides. It substantiates the revisionist argument that the divide between socialist women and liberal (or so-called ‘bourgeois’) feminists has been overstated and highlights international politics and the international peace movement as a particular sphere of collaboration between socialist and liberal women during feminism’s first wave.