Alexander Taggart McGill was born at Canonsburg, Pa., on February 24, 1807, the son of John and Mary Taggart McGill. After graduating from Jefferson College, then at Canonsburg, Alexander entered the Associate Presbyterian (Seceder) Seminary in Canonsburg, but for reasons of health, was forced to suspend his studies. Venturing south, McGill taught school at the Baldwin Academy in Milledgeville, Ga., and later studied law, gaining admittance to the Georgia bar in 1830. He was also appointed by the state legislature Surveyor of the Cherokee Land Reservation. In 1831, he returned to Canonsburg to resume his preparation for the ministry, and in 1835 was ordained by the Associate Presbyterian Synod at Carlisle, Pa., and installed as pastor of four small congregations.
The decade of the 1830s was a period of crisis in Presbyterian loyalties, and in 1838, McGill left the Associate Synod, transferring his membership to the Old School Presbytery of Carlisle. From 1842 to 1852, and 1853-1854, he was Professor of Ecclesiastical History and Church Government at Western Theological Seminary (now Pittsburgh Theological Seminary) in Allegheny, and for one year, 1852-53, he taught at Columbia Seminary in South Carolina. In 1854, the General Assembly (Old School) appointed him Professor of Pastoral Theology at Princeton Seminary, N.J., a chair he held until his retirement in 1883. He was author of many books and pamphlets, including several discussing the position of the Presbyterian Church with respect to slavery.
McGill became Moderator of the General Assembly (Old Style) in 1848, and was Stated Clerk from 1850 to 1870. His honorary degrees included a D.D. from Marshall College (1842) and an L.L.D. from the College of New Jersey (1868). He was married on May 18, 1837, to Eleanor A. McCulloch of Lewistown, Pa., and was father of three sons and three daughters. Nine years after Eleanor McGill died on March 6, 1873, McGill remarried to Catherine Bache Hodge of Princeton, who died on July 3, 1884. McGill died in Princeton on January 13, 1889.