This article examines the grassroots Black internationalist organizing of the British Black Panther Movement (BBPM). The BBPM, which was inspired, although not founded, by the U.S. Black Panthers, was a London-based antiracist movement composed mainly of Afro-Caribbean and South Asian immigrants to the United Kingdom. The British Panthers led hundreds of campaigns for housing, education, health, legal aid, employment and against police brutality from 1969 to 1973. These pages reconstruct the day-to-day organizing efforts of the BBPM, revealing a highly active movement that focused on bridging local people's experiences of racism with the movement's membership in diasporic networks. Analysis of oral histories and forty-four issues of movement newspapers collated from across six archives demonstrates that the BBPM also raised awareness of British institutional racism and police brutality in the absence of public recognition of these issues. In so doing, this article introduces significant new evidence about the nature and extent of anti-Black racist violence in Britain in the late 1960s and early 1970s and opens up novel perspectives on the forms of Black political mobilization in Britain. Among the UK's Black Power organizations, the BBPM was the most militant and secretive. Members rigorously studied Black history and literature and labor movement history inside communal spaces that the movement occupied in London. The BBPM also acted as an umbrella organization, facilitating a network of Black Power movements across the United Kingdom. While increasingly internationalist in its outlook, the movement splintered over time, with former members founding Black organizations dedicated to working-class people's concerns, intellectual life, and women's issues.