Sir William Middleton 5th Baronet (1738–1795), was a British soldier and politician who sat in the House of Commons from 1774 to 1795.

Middleton was the son of Sir John Lambert Middleton, 4th Baronet of Belsay Castle, a former merchant, and his wife Anne Perkins, a widow and daughter of Sir Nathaniel Hodges, and was born on 6 June 1738. He joined the Royal Horse Guards and was Cornet in 1756 and Lieutenant in 1759. He was severely wounded at the Battle of Minden on 1 August 1759, and was left lame for life. In 1762 he became captain. He succeeded his father in the baronetcy on 2 March 1768 and retired from the army in 1774. He married Jane Monck, daughter of Lawrence Monck of Caenby, Lincolnshire on 20 April 1774,^[1]

In 1774 Middleton was elected as Member of Parliament for Northumberland in a contested election when he came second in the poll. He promised to act an independent and disinterested part in Parliament and generally did so. He was re-elected in 1780, 1784 and 1790. He is reported as attending parliament infrequently and never spoke.^[1]

Middleton died on 7 July 1795.^[1]