John Thornhagh (1648–1723), of Fenton and Osberton, Nottinghamshire, was an English Whig politician who sat in the English and British House of Commons between 1689 and 1710. Thornhagh was baptized on 27 January 1648 at St Mary's Nottingham, the only son of Francis Thornhagh, MP for East Retford and his wife Elizabeth St Andrew, daughter of John St Andrew of Gotham, Nottinghamshire. He succeeded his father in 1648. He was admitted at Jesus College, Cambridge on 1 June 1664. He married Elizabeth Earle, the daughter of , of Stragglethorpe, Lincolnshire, on 15 September 1670.