This dissertation explores the role of moral imperialism in the late nineteenth century expansion of the British Empire using East Africa as a case study. Moral imperialism, the ideology that argued that the British had a moral duty to "civilize," "Christianize," "uplift," and economically "develop" non-Europeans and their territories, has not been taken as seriously by historians as other factors for British expansion, namely economic arguments and strategic geopolitics by British officials. By applying Alan Lester's model of three categories of colonial discourse in nineteenth century South Africa: governmentality, humanitarianism, and settler capitalism to East Africa between 1873 and 1901, I isolate moral imperialism (humanitarianism) as a contributing factor of imperialism, which is possible because the region had limited economic and geopolitical significance to the British Empire. Missionary, religious, civic, and anti-slavery organizations formed a moral lobby that actively interacted with and pressured government officials to increase Britain's activities and influence in Zanzibar, East Africa, and Central Africa thereby moving these areas from the informal empire to the formal empire. By analyzing how these moral imperialists, mainly upper and middle class men from the British and Foreign Anti-Slavery Society, Church Missionary Society, Universities' Mission to Central Africa, and the Imperial British East Africa Company communicated their positions on East African slavery, the slave trade, and other moral imperial issues to their members, their supporters, the general public, and the decision makers within the British government this dissertation analyzes moral imperialism's efforts to change the racial and labor dynamics as well as the transportation system of East Africa into something that was controllable by Europeans. This process, which took a generation, began with a series of treaties focused on combating the slave trade throughout the Indian Ocean, accelerated during the Partition of Africa and the jingoistic 1890s, and ended with the building of the Uganda Railroad and the birth of a white settler society in British East Africa at the turn of the twentieth century.