Thornhagh came of a wealthy family of Whig country gentlemen. His grandfather represented East Retford on his own interest from 1688-1705 and the county from 1705-10. Of his father, who never stood but played an influential part in county politics, Newcastle wrote: ‘My opinion has always been, ever since I knew Nottinghamshire, that if Mr. Thornhagh could be prevailed upon to stand, he would be the most proper person’.
He died 17 May 1787.
