Giles Firmin (1614–1697) was an English minister and physician, deacon in the first church in Massachusetts of John Cotton, and ejected minister in 1662.
The son of Giles Firmin, he was born at Ipswich. As a schoolboy he was impressed by the preaching of John Rogers at Dedham, Essex. He matriculated at Emmanuel College, Cambridge, in December 1629, his tutor being Thomas Hill. At Cambridge he studied medicine.
In 1632 he went with his father to New England. While at Boston, Massachusetts, he was ordained deacon of the first church, of which John Cotton was minister. At Ipswich, Massachusetts, he received in 1638 a grant of 120 acres (0.49 km2) of land. He practised medicine in New England, and was reputed a good anatomist. He married there Susanna, daughter of Nathaniel Ward, pastor of the church at Ipswich.
About 1647 he returned to England, leaving wife and family in America; on the way he was shipwrecked on the coast of Spain. In 1648 Firmin was appointed to the vicarage of Shalford, Essex, which had been vacant a year since the removal of Ralph Hilles to Pattiswick. At Shalford he was ordained a presbyter by Stephen Marshall and others.
A royalist in principle, he prayed for the afflicted royal family. He got into controversy on points of discipline. He was a strong advocate for the parochial system, insisted on imposition of hands as requisite for the validity of ordination, and denied the right of parents who would not submit to discipline to claim baptism for their children. With Richard Baxter he opened a correspondence in 1654, complaining to him about separatists. The Quakers also troubled his parish. In church politics he followed Baxter, preferring a reformed episcopacy to either the presbyterial or the congregational model, but laying most stress on the need of a well-ordered parish. He actively promoted in 1657 the "agreement of the associated ministers of Essex" on Baxter's Worcestershire model.