One of John Wesley's most able and loyal early associates, he graduated from Trinity College, Oxford in 1739 and obtained a medical degree in 1745. While teaching in Wales he made the acquaintance of Howell Harris and was caught up in the Welsh revival. Failing to get himself ordained, in 1746 he offered his services to Wesley, who used him intensively in London 1746-48, then as 'first master' at Kingswood School when it opened in 1748. Having served there through its difficult opening years, in 1752 he became Wesley's Assistant in the Bristol and Cornwall Circuits, then in the London Circuit as a curb to Thomas Maxfield 1758-67. In the early 1750s he married Sarah Perrin, Wesley's housekeeper at the New Room.
The Countess of Huntingdon failed to obtain a living and Anglican orders for him, but in 1764 he was ordained by Bishop Erasmus. For health reasons he left Methodism at the end of 1769, was ordained by the Bishop of London and became curate and, by 1780, vicar of Harwich. He remained on terms of warm friendship with both Charles and John Wesley, though the latter clearly regretted his 'defection'.