Ebenezer Gay, son of Nathaniel and Lydia Gay, was born and raised in Dedham, Massachusetts. After graduating from Harvard College in 1714, he studied for the Congregational ministry while teaching at schools in Hadley and Ipswich. In 1718 he was ordained minister of the First Church at Hingham, Massachusetts, a position he maintained for three months short of seventy years. During this time he married Jerusha, a great-granddaughter of Governor William Bradford, and with her raised eleven children.

During the Revolution, his political sympathies were Tory. In theology, however, he was noted for his Arminianism, a liberal and democratic intellectualism in religious doctrine. This stance, condemned by his Calvinist contemporaries because of its opposition to the doctrine of absolute predestination, was expressed in Gay's emphasis on the efficacy of free will, his forceful opposition to creeds, and in the rationalist and progressive ideas which appear throughout his sermons. In Natural Religion, as Distinguish'd from Revealed ... (1759), for example, Gay postulates a Newtonian universe from which man's unaided natural reason can deduce ethical principles and the attributes of deity. Other published sermons include A Beloved Disciple of Jesus Christ Characterized ... (1766), preached on the death of Jonathan Mayhew, whose liberal views Gay helped shape, and another, preached on the text "And now, lo, I am four score and five years old" (1781), which was published repeatedly as The Old Man's Calendar ... (1781). Gay died at Hingham in 1787.

Gay is considered to be the founder of American Unitarianism because of his influential leadership in the establishment of free inquiry and a set of opinions distinct from Calvinism.