Andrew Todd McKinney, son of Nancy W. (Todd) and Samuel McKinney, was born on March 18, 1838, in Randolph County, Illinois. In 1850 he moved with his family to Huntsville, Texas, where he attended Austin College, of which his father was president. After graduating from Princeton University in 1858, he studied law with his uncle, Judge Robert J. McKinney, in Knoxville, Tennessee, where he was admitted to the bar. He did educational work in Louisiana and served briefly with a Louisiana regiment in the Confederate Army before he began to practice law at Huntsville in January 1866. His public career began with membership in the Constitutional Convention of 1875. He was a member of the Eighteenth, Nineteenth, Twenty-second, Twenty-fourth, Twenty-ninth, Thirtieth, Thirty-first, and Thirty-second Texas legislatures. He served on the committees on education and on investigation of the International-Great Northern Railroad. McKinney was a member of the original board of regents of the University of Texas and president of the board of directors of Sam Houston Normal College (now Sam Houston State University).
On September 16, 1882, McKinney married Mary Louise Hill; they had four children. McKinney died on May 7, 1931, in Huntsville, where he was buried in Oakwood Cemetery. He was an active Presbyterian, a Mason, and in 1875 was grand master of Texas Odd Fellows.