Born in Boston and christened by William Ellery Channing, William Channing Gannett spent four years helping semi-starved freed slaves in South Carolina before he was ordained and began to serve in the West. He began in then muddy Milwaukee in 1868, and later served at Unity Church in St. Paul, Minnesota, before moving on to Rochester, New York, where Susan B. Anthony was a member of the congregation. In order to raise the funds required to allow admission of women to the University of Rochester, she pledged her life insurance, while Gannett and his wife, Mary, a birthright Quaker, pledged their house.

He wrote hymns celebrating life such as “Bring, O morn, thy music.” He facilitated action for his Unitarian Church and Rochester’s Temple Berith Kodesh jointly to establish the Boys Evening Home, where newsboys of all faiths could socialize and learn arts and crafts.

William Channing Gannett was known as a Western radical. Nevertheless the American Unitarian Association affirmed and distributed his statement of "The Things Most Commonly Believed Today Among Us."

Frank Lloyd Wright wrote The House Beautiful, a volume based on an essay by this Unitarian minister.