Mill was the second son of Sir John Mill, 3rd Baronet of Woolbeding and his wife Margaret Grey, daughter of Thomas Grey of Woolbeding.
[1] Mill was brought in by the Duke of Somerset to fill a vacancy at Midhurst and was returned unopposed as Member of Parliament at a by-election on 6 November 1721.
He was returned unopposed for Horsham at the 1741 general election by the 7th Viscount Irwin at the request of the Duke of Newcastle.
He had four sons Richard, John, Henry, and Charles who succeeded to the baronetcy in turn.
His five daughters were Margaret, Philadelphia, Elizabeth, Mary and Martha.