The son of Maturin Ballou, a Baptist minister, he was self-educated and devoted himself early on to the ministry. In 1789 he converted to Universalism and in 1794 became a pastor of a congregation in Dana, Massachusetts.
He preached at Barnard, Vermont and surrounding towns in 1801—1807; at Portsmouth, New Hampshire, in 1807—1815; at Salem, Massachusetts, in 1815—1817; and as pastor of the Second Universalist Church in Boston from December 1817 until his death there on the 7th of June 1852.
He founded and edited The Universalist Magazine (1819; later called The Trumpet) and The Universalist Expositor (1831; later The Universalist Quarterly Review) and wrote about 10,000 sermons as well as many hymns, essays and polemic theological works. He is best known for Notes on the Parables (1804), A Treatise on Atonement (1805) and Examination of the Doctrine of a Future Retribution (1834). These works mark him as the principal American expositor of Universalism.
Ballou has been called the "father of American Universalism," along with John Murray, who founded the first Universalist church in America. Ballou, sometimes called an "Ultra Universalist," differed from Murray in that he divested Universalism of every trace of Calvinism and opposed legalism and trinitarian views.