Seth Shepard McKay, professor and specialist in Texas constitutional and political history, the son of Albert Johnson and Jane Elijah (Sparks) McKay, was born on January 12, 1888, at Holland, Texas. He graduated from Holland High School in 1905 and attended Baylor University for two years (1905–06, 1908–09) before earning a B.A. in history from the University of Texas in 1912 and an M.A. in 1919. In 1924 he received the Ph.D. cum laude from the University of Pennsylvania. He was principal and coach at Sparks Public School from 1906 to 1908, and later a teacher and coach at Peacock Military Academy (1912–13) and at San Marcos Baptist Academy (1913–14). McKay taught at North Texas State Teachers College (now the University of North Texas) between 1916 and 1921. He was adjunct professor of history at the University of Texas in 1922–23 and lecturer at Ohio State University in 1923–24.
After obtaining his doctorate McKay was professor and head of the department of history at Furman University in Greenville, South Carolina, for four years. From 1928 until his retirement in 1965, except for visiting appointments at the University of Texas in 1948–49 and the summers of 1947 and 1949, he was professor of history at Texas Technological College (now Texas Tech University). From 1939 until 1944 he served as head of the department. McKay was a popular teacher, and his office was usually crowded with students seeking academic help or counseling. He also was a prolific, but meticulous and objective, scholar. His publications number seven books and eighty-three articles, including sixty-five for the Handbook of Texas. He was the author of Making the Texas Constitution of 1876 (1924); Debates in the Texas Constitutional Convention of 1875 (1930); Seven Decades of the Texas Constitution of 1876 (1942); W. Lee O'Daniel and Texas Politics, 1938–1942 (1944); Texas Politics, 1906–1944 (1952); Texas and the Fair Deal, 1945–1952 (1954); and (with Odie B. Faulk) Texas After Spindletop (1965).
McKay was a member of the Texas State Historical Association, West Texas Historical Association, American Historical Association, Mississippi Valley Historical Association, American Political Science Association, and Southwestern Social Science Association. He was president of the West Texas Historical Association during the 1954–55 term. He was active in the Democratic party and served as a deacon at the First Christian Church in Lubbock. On October 21, 1914, he married Bama Lawson Camp of San Antonio, the daughter of a prominent Texas senator and district judge. The couple had three children, two of whom survived to adulthood. McKay died on June 4, 1969, and was buried in Resthaven Memorial Park Cemetery, Lubbock.