He served for fifty years as minister of the Second Congregational Church (Unitarian) in Worcester, Massachusetts, formed after the town voted not to call Bancroft to its First Parish due to his liberal persuasion. Aaron Bancroft held that Jesus Christ was morally heroic but not divine. In 1807 he published his Life of General Washington. He served as the first president of the American Unitarian Association. The noted American historian, George Bancroft, was his son.