Thomas had been M.P. for Lewes in 1768 in the Duke of Newcastle's interest. He married firstly Catherine, the daughter of General David Graeme of Braco Castle, Perth, who died in 1804, and secondly Jane Maria, daughter of George Brown of Ellistoun but had no issue by either wife.

Lord Hampden and his first wife were attacked in The Female Jockey Club (1794) 'but the most serious charge against him is his having left the Whigs on the outbreak of the French Revolution, and against her that she was languid and insipid and addicted to musical parties and cardplaying.' Lady Hampden's portrait by Gainsborough hangs in the gallery at Glynde Place. Thomas died in 1824 and his brother John, who had been a diplomatist, British Minister at Munich, 1780, and at Turin, 1783-98, succeeded to the title only to die three weeks later, also without heirs.