In 1705 Pitt was returned as Member of Parliament for Old Sarum, a pocket borough controlled by his family. He retained the seat at the 1708 general election, but in 1710 was not put forward by his father and was returned instead on his own account as MP for Salisbury. He came third in the poll at Salisbury at the 1713 general election but his father then put him up at Old Sarun again where he was returned. At the 1715 general election Pitt stood for Parliament at Old Sarum and Salisbury but was only returned for Old Sarum. At the 1722 general election he stood at Old Sarum and Okehampton, and chose to take the seat at Okehampton, where he remained until his death. Unlike the rest of his family, who were Whigs, Robert Pitt became a Tory possibly partly in resistance to his domineering Whig father.Brown p. 17
