This paper examines the historical developments and the debates revolving around the formation of an Ottoman–Iranian alliance in the Ottoman Empire in the aftermath of the 1908 Revolution. It argues that although neither the idea of an alliance between the two states nor the attempt to establish it was new, the way it was discussed, justified, and promoted in this period was different. The previous attempts by the Ottomans were led by the state as part of a broader pan-Islamist project (ittihad-ı İslam) that adopted a heavily religious tone. On the other hand, the main proponents of the alliance during the constitutional period were mostly transnational/international figures and religious scholars, who framed the issue within the context of Ottoman–Iranian relations, focusing on immediate pragmatic, strategic, and ideological concerns, such as protecting the sovereignty and security of the two countries against European imperialism through constitutionalism. Rather than focusing on reconciling the disputes between the Sunnis and Shi’is, and presenting this alliance as the first step towards the formation of a broader Islamic union as Abdülhamid II did in the nineteenth century, these people emphasized brotherhood and solidarity between the two constitutional governments, and tried to establish a strategic partnership based on shared borders, experiences, ideals, and enemies.