This thesis examines the relationship between practices of internationalism, patterns of racialisation, and the politics of anti-racism and anti-imperialism in the revolutionary Marxist left in Britain between 1899 and 1933. I focus on two organisations, the Social Democratic Federation and the Communist Party of Great Britain, examining how different racialised subaltern populations were represented in their publications and how this affected the anti-imperial advocacy and activism of these political groups. I am interested in how the writings of colonial nationalists, as well as the intervention of transnational activists, helped to shape this political praxis. The thesis begins with a study of how positive racialisations, developed by colonial activists as a discursive means to argue for the inapplicability of the âcivilising missionâ to their respective societies, were drawn on by SDF activists and figureheads such as HM Hyndman to bolster their increasingly oppositional stance towards the British Empire. Further chapters demonstrate how groups of border-crossing racialised outsiders, be they Russian-born Jews in the SDF or Indian activists in the CPGB, utilised a strategic universalism to overcome their marginalisation within the ranks of the revolutionary Marxist left, and to gain support for their respective communal concerns. During the course of the time period covered within the thesis, the October Revolution, the rise of the Bolsheviks, and the foundation of the Comintern helped to reshape analyses of imperialism as well as practices and theories of internationalism on the British far-left. Particular attention is given to how activists either attempted to utilise or bypass this âofficial internationalismâ to promote their own international anti-imperial networks and discourse, and the efficacy of their efforts. It is my hope that this study will be able to shed light on international influences on the British Marxist left beyond the Continental, provide a greater nuance to histories of Marxism and race in Britain, and demonstrate the variety of models and practices of internationalism available to these activists in the early years of the twentieth century.