 Shirley entered Parliament in 1742 at Brackley, on the interest of the 1st Duke of Bridgewater, who had withdrawn his support from George Lee after the latter accepted office in the Carteret Ministry.He followed his patron in backing the opposition under Robert Walpole.After the death of Bridgewater in 1744 and the transfer of the Brackley interest to Sir Richard Lyttelton, who married Bridgewater's widow in 1745, Shirley conformed with Lyttelton's politics to support Henry Pelham's ministry.