From The Unitarians and the Universalists by David Robinson (324):

SULLIVAN, WILLIAM LAURENCE (15 November 1872, East Braintree, MA-S October 1935, Germantown, PA). Education: Bachelor of Philosophy, St. John's Ecclesiastical Seminary, Brighton, MA, 1896; S.T.B., Catholic University of America, 1899; licentiate in sacred theology, Catholic University of America, 1900. Career: Admitted to Missionary Society of St. Paul the Apostle, 1899; Paulist mission preacher, 1899-1901; ordained to Catholic priest-hood, 1899; served at St. Thomas's Church, Washington, DC, 1900-1907; professor of theology, St. Thomas College, Washington, DC, 1902-6; pastor, Paulist Church, Austin, TX, c. 1907-9; writing and tutoring, Kansas City, MO, and Cleveland, OH, 1909-10; became a Unitarian, 1911; teacher, Ethical Culture School, New York, 1911-12; minister, All Souls Unitarian Church, Schenectady, NY, 1912-c. 1913; associate minister, All Souls Unitarian Church, New York, 1913-15; minister, 1915-22; mission preacher, Unitarian Laymen's League, 1922-24; minister, Church of the Messiah, St. Louis, MO, 1924-28; Germantown, PA, Unitarian Church, 1929-35.

William Laurence Sullivan was one of the chief advocates of Christian theism in twentieth-century Unitarianism. But the development of his final identity as a Unitarian minister was a difficult and painful process. Sullivan was from his early years a devout Roman Catholic and was ordained to the Catholic priesthood in 1899, serving as a Paulist mission preacher and then a professor of theology. His unwavering commitment to his faith and his religious vocation was broken by the 1907 encyclical of Pope Pius X condemning modernism. Even though Sullivan described Catholicism as "deeply rooted in the home soil of my nature," he could not with complete honesty continue in the church under the conditions laid down by the papal encyclical (Under Orders, p. 135). In his autobiography he called his anguished struggle over this issue a conflict between "heart's love" for the settled faith and the challenge of the active mind, and he stressed his rejection of the doctrine of papal infallibility as a major factor in his growing doubts about the church (p.135). In his intellectual search he was influenced by the writings of the English Unitarian leader James Martineau. In 1911 he became a Unitarian and entered the Unitarian ministry in 1912. 

Sullivan's later career was distinguished. He was one of the most effective pulpit orators in the denomination and held notable pastorates at New York City and Germantown, Pennsylvania. His identity within the denomination was based upon his unyielding theism and his scornful rejection of the Humanist movement. As Sullivan saw them, the Humanists were atheists or agnostics who were unwilling to accept that designation, styling themselves Humanist to preserve their respectability in, a church that historically had been Christian. Sullivan led an unsuccessful fight to secure a theistic affirmation at a meeting of the National Conference in 1921. His theological creed began much in the tradition of William Ellery Channing and Ralph Waldo Emerson with an affirmation of the moral nature of the personality: "I am a moral personality under orders" (p. 159). This moral imperative was a "via sacra" that led to the theistic faith that he espoused (p.160).

Bibliography

A. Letters to His Holiness Pope Pius X (Chicago, 1910); The Priest: A Tale of Modernism in New England (Boston, 1911); From the Gospel to the Creeds: Studies in the Early History of the Christian Church (Boston, 1919); "God, No-God, Half-God," Christian Register, 100 (August 8, 1921), 775-76; Epigrams and Criticisms in Miniature (Philadelphia and London. 1936); Under Orders: The Autobiography of William Laurence Sullivan (New York. 1944).

B. Biographical sketch in Epigrams and Criticisms in Miniature (see above); Under Orders (autobiography) (see above).