During the 1960s, the Malaysian prime minister, Tunku Abdul Rahman, struggled to establish the ‘Muslim Commonwealth’, an organization of Muslim-dominated sovereign states. This international programme for Muslim unity was particularly significant because it offered an opportunity for an unexpected player from outside the Islamic heartlands of the Middle East and South Asia to seize the leadership of the global religious community. This article recovers the project’s genealogy, objectives, and reception. In the global context of decolonization and the Cold War, the Tunku looked to the British-led Commonwealth of Nations to model this pan-Islamic institution in an attempt to promote cooperation, development, and peace among Muslims. He deployed a range of idioms to broaden the appeal of the Muslim Commonwealth, drawing from different intellectual genealogies and from an international circuit of ideas prevalent during decolonization. The eventual failure of the Tunku’s project exposes the hierarchies and rivalries in South–South relations during the decade and reveals how Malaysian-led pan-Islamism remained bound to the post-colonial condition of the nation-state.