[1] In 1751 he succeeded to the estates of his uncle the Earl of Shelburne (who had died childless) and assumed by Act of Parliament the surname of Petty in lieu of his patronymic.
In 1754 he bought Bowood Park, an estate between Chippenham and Calne in Wiltshire, and rebuilt the mansion there.
[1] In 1743 he entered the Irish House of Commons as one of two representatives for County Kerry, a seat he held until 1751.
[1][4] He was Governor of County Kerry in 1754[1] and the same year he was returned to the British House of Commons for Wycombe, a seat he held until 1760.
He was succeeded in the earldom by his eldest son, William, who became Prime Minister of Great Britain and was created Marquess of Lansdowne in 1784.