Leinster was a member of the Irish House of Commons for Athy from 1741 before succeeding his father as 20th Earl of Kildare in 1744 [REF].
In 1761 Lord Kildare was created Earl of Offaly and Marquess of Kildare in the Peerage of Ireland and in 1766 he was further honoured when he was made Duke of Leinster, becoming by this time the Premier Duke, Marquess and Earl in the Peerage of Ireland [REF].