The son of a Hampshire parson also named John James, he attended the Holy Ghost School, Basingstoke, of which his father was headmaster. He was then apprenticed in 1690 to Matthew Banckes, Master Carpenter to the Crown 1683–1706, whose niece he married, and he lived for a while at Hampton Court Palace. He was employed at Greenwich, where in 1718 he became joint Clerk of the Works with Hawksmoor, whom he succeeded as Surveyor of the Fabric of Westminster Abbey, where he completed Hawksmoor's west tower. In the interim he was appointed master carpenter at St. Paul's Cathedral, where he assisted Sir Christopher Wren and succeeded him in 1723 as Surveyor of the Fabric of St Paul's Cathedral. He was Master of the Carpenters' Company in 1734.