William Henry Abdullah Quilliam (1856-1932) was a late nineteenth-century British convert to Islam who led the Liverpool Muslim Institute (LMI; 1887-1908) – at once mosque, charity, a center for propagating Islam and educating Muslims, and a publishing house. In the United States, Mohammed Alexander Russell Webb (1846-1916) established a similar, short-lived Islamic institution called the American Islamic Propaganda (AIP; 1892-1896) as well as journals to spread Islam in the United States. Scholarship on these two early converts and their institutions have relied on English sources to place them within British and American religious, cultural, and historical contexts while using accounts from Quilliam and Webb themselves to draw connections to Ottoman state officials, Sultan Abdülhamid II (1842-1918), and Muslim thinkers of the day. This dissertation undertakes a more comprehensive, critical, and reciprocal examination of these relationships to converts and their communities, with a focus on the Ottoman side. Drawing on records in Ottoman state archives and on Ottoman Turkish and Arabic printed materials, I argue that Ottoman diplomats, Sultan Abdülhamid II, and Arab and Turkish Muslim intellectuals often cultivated relationships and disseminated news about American and British converts to Islam to advance their diplomatic, geopolitical, and religious ends. At the same time, they followed with interest how Muslim culture developed, sometimes in distinctive or idiosyncratic ways, within the British and American environments in which Quilliam and Webb worked. In short, this dissertation examines the late Ottoman state’s pursuit of geopolitical interests and “image management” during a period of intensifying diplomatic and cultural engagements with the English-speaking world, while considering how Muslim intellectuals looked to Western converts as an affirmation of the universalist appeal and relevance of Islam in a period of high Western imperialism. The story of these two converts and their communities thereby cast light on topics relating to Ottoman diplomacy, pan-Islamism, the emerging idea of the Muslim world, and transnational Muslim thought during the late nineteenth and early twentieth centuries.