This article explores the history and development of British manifestations of a Black diasporic anti-colonial anti-fascist political tradition that stretches across the twentieth century. It centers the experiences and reflections of Black activists and intellectuals in Britain, exploring their efforts to theorize about fascism as a manifestation of white supremacy. The article explores what we can learn about British society and political culture by returning to the overlooked and excluded experiences of Black British activists and intellectuals—in particular, their theoretical and physical encounters with what they called British “fascism” from the 1930s to the 1970s. Journeying from interwar anti-colonial Marxist political writing, Black periodicals in the 1950s and 1960s, to the publications of the British Black Power movement, the article ultimately argues that these encounters confront historians of modern Britain with a different and generative way of thinking about British racism and British fascism in relational terms.