This article aims, first, to argue that fandom matters to politics and, second, to offer a theorisation of what I call politicised fandom. The article proceeds through three stages. Part 1 offers a brief mapping of the existing scholarship within the interdisciplinary sub-field of fan studies and alights on a definition of fandom offered by Cornel Sandvoss, before mapping some different understandings of the fandom-politics relation. Here, I argue for an emphasis on the agency and capacity of fan communities to intervene politically. Part 2 then provides an initial theorisation of politicised fandom, highlighting four key elements: productivity and consumption, community, affect and contestation. Part 3 offers some snapshots of how this politicised fandom is manifest empirically via the analysis of three similar yet different instances of politicised fandom in UK left politics: Russell Brand, Milifandom and Corbyn-mania.