This article investigates the relationship between the coalitional structure of revolutionary movements and revolutionary outcomes. Noting the chimerical nature of revolutionary coalitions, it introduces readers to the concept of ‘movement split’: the moment in a revolutionary process when, once a regime is overthrown, the revolutionary coalition fractures into ‘radicals’, who seek further, social revolution; and ‘conservatives’ who are satisfied with a limited, political revolution. By means of a comparative historical analysis of the 1789 French Revolution and 2011 Egyptian Revolution, it analyses the role of coalition structure in determining revolutionary outcomes after movement split. In both cases, the distribution of mobilizing capacity between radicals and conservatives was the key factor determining whether each revolutionary movement came to pursue a ‘political’ or ‘social’ revolutionary’ program. Where conservatives retained control over mobilization, advancement of the revolutionary process ended once political revolution was achieved, while when radicals retained control, a process of social revolution was undertaken. Thus, when seeking to anticipate the trajectory of change an emergent revolutionary movement is liable to undertake, it is fruitful to examine whether it is radicals or conservatives who control its principal mobilizing structures.