This article traces the history of the commemoration in Britain, India, and America of leading Bengali religious and social reformer, Rammohun Roy, from his death in Britain in 1833 through to the publication of the first substantial account of his life and work in 1900. It reveals the vital part that commemorative processes played in creating a sense of imagined community among liberal religious groups who were in the vanguard of social reform movements in India, Britain, and the United States. The groups under consideration are the Brahmo Samaj, an organization founded by Roy to reform Hinduism, and Unitarians, Protestant dissenters who rejected the orthodox Christian doctrine of the Holy Trinity and the evangelical approach to missionary work. Bridging the study of transatlantic and imperial networks, the article explores a culture of commemoration that emphasized affinity rather than difference between groups whose members were unequally positioned in colonial discourse as on opposite sides of the colonizer–colonized, Hindu–Christian, and East–West divides. It exposes the commemoration of Roy as a complex and contested process, creating both ‘localized’ and ‘globalized’ collective memories. These reveal the possibilities for, and limitations on, cross-cultural interchange in an age of global Christian mission and British imperial power.