The son of Coulson Fellowes of Ramsey Abbey, Huntingdonshire, and his wife, Urania Herbert, William Fellowes matriculated at St John's College, Cambridge in 1744, aged 17.
[1][2][3] Fellowes entered parliament in 1768 as member for Ludlow: his mother's brother, Henry Herbert, 1st Earl of Powis, brought him in unopposed with his local interest.
He generally supported the administrations of Augustus FitzRoy, 3rd Duke of Grafton and Lord North.
He returned to parliament in 1784 for Andover, once more unopposed, backed by John Wallop, 2nd Earl of Portsmouth, married to his sister Urania.
[1] Fellowes died on 10 February 1804 in Grosvenor Street, London.