Parker, Theodore,1810–60, American theologian and social reformer, b. Lexington, Mass. He graduated from Harvard Divinity School in 1836 and was pastor (1837–46) of the Spring Street Unitarian Church, West Roxbury, Mass. The liberalism that he presented in Boston in 1841 and amplified in his scholarly Discourse of Matters Pertaining to Religion (1842) was then so radical that the Boston Unitarian clergy withdrew from him, although he remained a member of their association. He was one of the transcendentalists, contributed to the Dial, and edited (1847–50) the Massachusetts Quarterly Review. In 1845 he became preacher of the Twenty-eighth Congregational Society of Boston. His congregation grew to 7,000. In addition he lectured at lyceums throughout the country and was a leader in antislavery and other reform activities. In 1859 ill health forced him to retire, and he died in Florence. After his death Parker's works were widely read, and his once radical views gained acceptance. The best edition of his works is the Centenary (15 vol., 1907–13).
See J. Weiss, The Life and Correspondence of Theodore Parker (1864, repr. 1969); biographies by O. B. Frothingham (1874) and H. S. Commager (1936, repr. 1960); J. W. Chadwick, Theodore Parker, Preacher and Reformer (1900, repr. 1971); J. E. Dirks, The Critical Theology of Theodore Parker (1948, repr. 1970).