The four decades that span the collapse of British imperial authority in the American colonies in 1774, to the disintegration of the Napoleonic Empire in 1815 witnessed unfathomable social and political change. There emerged a transformation from one ‘type’ of time to another: a change in the nature of change itself. Following the onset of the American and French Revolutions, time became more than a constitutive element in the lived experience of history – it also became the chief assassin of political legitimacy. Widespread considerations and perceptions of time in both American and French revolutionary contexts complicated and deranged the efficacy of power. Drawing upon contemporary temporal theories to explain how legitimate political authority eroded (before revolution), remained unstable (during revolution), and was finally reassembled (after revolution), this thesis presents two empirical case-studies for assessing the validity of German historian Reinhart Koselleck’s thesis, and other’s, regarding temporality and historicity. Although Koselleck’s viewpoint is largely dependent upon anecdote and abstraction to support theoretical observations, this thesis explores the application of time conceptions to five sites of political contestation: (1) the peculiar historicity of the ancien regime, which contributed to its own collapse by producing a time temperament that desensitised it to political urgency; (2) deliberative processes of the early Revolutions and the way in which time was transformed from an absolute or constant conceptual presence into an historical actor in its own right; (3) experimentations with time and history that were both a response to, and an attempt to rectify, the instability of political power during the mid-1780s in America and the early-1790s in France; (4) manipulations of revolutionary historical experience as a strategy for justifying the quasi-legal enterprises of the Constitutional Convention, 1787, and the coup of Brumaire, 1799; and (5) a comparative analysis of the interaction between power politics and temporality under the administration of George Washington and the Napoleonic Empire.