 Born in Marlboro County, South Carolina, on December 9, 1812, Thornwell graduated from South Carolina College at nineteen, studied briefly at Harvard, then entered the Presbyterian ministry starting at the Waxhaw Presbyterian Church.He became prominent in the Old School Presbyterian denomination in the south, preaching and writing on theological and social issues.He taught at South Carolina College, eventually served as its president, and went on to teach at Columbia Theological Seminary.