He was born at Northiam, in Sussex, and educated at Magdalen College, Oxford, where in 1612 he became a Fellow. In 1617 and 1621 the college allowed him to act as chaplain to Sir John Digby, ambassador in Spain. In Madrid he preached a sermon that pleased Prince Charles, afterwards Charles I, and the latter on his accession appointed Frewen one of his chaplains.
In 1625 he became canon of Canterbury Cathedral and Vice-President of Magdalen College, and in the following year he was elected President. He was Vice-Chancellor of Oxford University in 1628 and 1629, and again in 1638 and 1639. It was mainly by his instrumentality that the University plate was sent to the king at York in 1642.
Two years later he was consecrated Bishop of Lichfield and Coventry, and resigned his presidentship. Parliament declared his estates forfeited for treason in 1652, and Cromwell afterwards set a price on his head. The proclamations, however, designated him Stephen Frewen, and he was consequently able to escape into France. At the Restoration he reappeared in public, and in 1660 he was consecrated Archbishop of York. In 1661 he acted as chairman of the Savoy conference.
