Percy’s early life was overshadowed by the incarceration, after the Gunpowder Plot, of his father, the 9th earl of Northumberland, who was not released from the Tower until 1621.
Percy was chosen to represent Marlborough in 1628 after Sir Francis Seymour plumped for Wiltshire in the third Caroline Parliament. The following year a correspondent of Dudley Carleton*, Viscount Dorchester, attributed the election to Percy’s brother-in-law, the 2nd earl of Leicester (Sir Robert Sidney*), ‘presuming he would have run the same way as they did that hated the duke’ [Buckingham]. Percy dined with Leicester in March 1628, but it is likely that the 2nd earl of Hertford (William Seymour*), the dominant patron in Marlborough, required little prompting to nominate Percy, who was first cousin to Hertford’s wife.
Percy travelled abroad after the Parliament, in the words of his father ‘as a younger son, and not in pomp’. He was visiting Paris in January 1631, but returned to England soon after to seek office.
Percy was returned at both elections in 1640 on his brother’s interest, sitting for Portsmouth in the Short Parliament and for Northumberland in the Long, but was expelled from the latter after his involvement in the first Army Plot. He escaped overseas, but returned to fight in the Civil War, when he commanded the king’s artillery and received a peerage. An inveterate intriguer, widely distrusted and, according to Clarendon, ‘generally unloved, as a proud and supercilious person’, he was eventually dismissed from the king’s service. He was arrested for corresponding with the parliamentarians in January 1645, but was soon released, although obliged to go into exile again. Remaining active in the royalist cause, he was appointed lord chamberlain by Charles II in 1653. He died, unmarried, in Paris six years later, having apparently burnt his papers.
