Divided cities are defined by a violent conflict of ethnonationalism and characterized by semi-permanent ethnic cleavages, high levels of endogamy and social segregation. Yet the perception that divided cities are wholly framed by the politics of ethnic homogeneity is challenged by a number of its citizens who refuse to be interminably circumscribed by ethnic politics. These ‘actors’ mobilize in social movements that promote non-sectarian politics and identities. They also include the protests of environmentalists, trade unionists and the celebrations of gay groupings. This article critically explores how such urban social movements may help ameliorate or contest the politics of ethnic antagonism in divided cities. It explores this issue in the context of debates regarding peacebuilding projects in divided cities, especially those that promote accommodative solutions to ethnic conflict, and shows how social movement mobilization may augment political power sharing. Focusing on non-sectarian social movement mobilization in Belfast, Northern Ireland, the article critically analyses movements in three ways: creating intercommunal networks; fostering a public sphere of debate; and challenging the programmed uses of segregated space.