This thesis examines the political development of County Mayo during the years 1780-1830, through the lens of its leading political dynasty, the Browne family of Westport.The two central characters are John Denis Browne (1756-1809), third Lord Altamont and first marquess of Sligo, and his brother Denis Browne (1763-1828), long serving MP for the county and leading magistrate. By unlocking the personal and political history of the Brownes, the most economically powerful and politically influential family in the region, it is possible to identify and examine changing patterns of governance in Ireland. The public lives of the Brownes coincided with a gradual shift away from the patrician and paternalistic model of local governance towards a more centralised pattern emanating from Dublin and London. Their political biographies cover pivotal stages in Irish history during the late eighteenth and early nineteenth centuries; the ongoing Catholic question, the suppression of radicalism in the 1790s, the Union and manifestations of agrarian insurgency and poor relief. Throughout this period, the Brownes were in constant contact with senior officials in Dublin and this, often tense, relationship revealed a growing divergence between the ruling elite of Mayo and official government policy. The appointment of Robert Peel as Chief Secretary in 1813 intensified this divergence as the maintenance of law and order, for centuries the reserve of local gentry figures, was brought further under the direct control of Dublin. As county Mayo moved from being a domain, controlled by a hand full of powerful families (the Brownes, Binghams, Cuffes, Dillons), to a more accessible and provincial part of the wider United Kingdom, the Brownes’ political ambitions began to gradually recede, their political hegemony and influence eventually being replaced by the state and an emerging Catholic bourgeoisie in the wake of Emancipation.