McDonald received his primary and secondary education in Texas schools, his Bachelor of Science degree from Lamar University in Beaumont, his Master of Arts degree from Rice University in Houston, and his doctorate from Louisiana State University. His dissertation on Jedediah Hotchkiss, Stonewall Jackson's topographer, later published as Make Me a Map of the Valley, was a Civil War History Book Club selection, and was named to the Civil War Times Illustrated's list of the one hundred best book on the Civil War. In addition to teaching and writing, McDonald served as executive director of the East Texas Historical Association and as editor of its journal. He was also a past president of the Texas State Historical Association, served as chairman of the Texas Committee for the Humanities, a member of the advisory board for the National Registry of the Texas Historical Commission, and was member of the Texas Sesquicentennial Commission.
