Brabazon, whose family was Norman in origin, was descended from Sir William Brabazon (d. 1552), vice-treasurer of Ireland, whose son Edward, Member for county Wicklow in 1585, was created Lord Brabazon, baron of Ardee in 1616, and whose grandson William became earl of Meath in 1627. In the eighteenth century the 5th to 9th earls represented county Dublin and (in some cases) county Wicklow, where they held high local offices, before succeeding to the peerage.
Although it was his elder brother Lord Ardee who was considered a possible candidate in the autumn of 1822, when a vacancy occurred for county Dublin, according to newspaper speculation in 1824 and 1825 it was the recently of age William who was apparently prepared to stand on their father’s interest in the event of a dissolution.
The Wellington administration declined to give him its support while the sitting Members persisted, but he offered at the general election of 1830, when he declared that he would follow his father’s principles and called for economies and tax reductions; after Richard Wogan Talbot had retired, he was returned in first place with Henry White following a contest against a Protestant Tory.
Returned unopposed as a reformer at the general election that spring, he signed the requisition for a county meeting on reform, 28 May 1831.
