He graduated from Harvard in 1798 and, struggling with French radicalism and Calvinist orthodoxy, found peace in a gentle, loving relationship with God. However, the struggle continued through two years during which Channing lived in Richmond, working as a tutor. Like many other great Christians (Luther, Wesley and others) he came to his definitive faith through much spiritual turmoil.
In 1803 Channing became pastor of the Federal Street Church in Boston, where he remained for the rest of his life. He lived through the increasing tension between religious liberals and conservatives and took a moderate position, rejecting the extremes of both groups.
Nevertheless he became the primary spokesman and interpreter of Unitarianism when he preached the ordination sermon of Jared Sparks in Baltimore in 1819; it was entitled Unitarian Christianity. In that address he explicated the distinctive tenets of the unitarian movement, only one of which was the rejection of the Trinity.
Other important tenets were the belief in human goodness and the subjection of theological ideas to the light of reason.
A few years later came another ordination sermon, entitled Likeness to God. The idea of human potential to be like God, although entirely scriptural, was seen as heretical by the Calvinist religious establishment of his day.
In later years Channing often preached against slavery, although he was never an ardent abolitionist. This middle position characterized his attitude about most questions, although his eloquence and strong influence on the religious world incurred the enmity of many extremists.
Channing had enormous influence over the religious (and social) life of his day, although his fame has waned in recent times, partly because many of his 'revolutionary' ideas have become commonplace.