This paper develops spatial dialectics as an analytical method capable of exposing and explaining the contradictions, dilemmas and tensions that cut through the spatialities of social movements. Despite scholarly recognition of internal divides in movements such as Occupy, there is greater need to conceptualise the inherently contradictory nature of social movements, in particular by reflecting on the role of spatiality. Building on recent work on multiple spatialities of activism, the paper shifts attention to contradiction as a key factor in spatial mobilisation, further arguing that the recent turn to assemblage thought is ill equipped for such a task. Dialectics is introduced via Bertell Ollman's influential account of its ontological and epistemological bases, before turning to Edward Soja's reading of Henri Lefebvre to incorporate spatiality. Spatial dialectics disrupts the linearity of thesis–antithesis–synthesis, placing contradictions not only within the historical unfolding of relations but also within co‐dependent yet antagonistic moments of space, through Lefebvre's ‘trialetic’ of perceived, conceived and lived space. Building on ‘militant research’, which combined a seven‐month ethnography, 43 in‐depth interviews and analyses of representations of space, spatial dialectics is put to work through the analysis of three specific contradictions in Occupy London's spatial strategies: a global movement that became tied to the physical space of occupation; a prefigurative space engulfed by internal hierarchies; and a grassroots territorial strategy that was subsumed into logics of dominant territorial institutions. In each case, Occupy London's spatial strategies are explained in the context of unfolding contradictions in conceived, perceived and lived spaces and the subsequent dilemmas and shifts in spatial strategy this led to. In conclusion, the paper highlights broader lessons for social movements’ spatial praxis generated through the analysis of Occupy London.