Raised in Cleburne, Texas, McWilliams' long tenure with the Longhorn football program started as a player from 1961 to 1963, when he helped the team compile a record of 30–2–1.
After graduating, McWilliams served two years as an assistant coach at Abilene High School in Texas, and in 1966, became one of the state's youngest head coaches, carving out a record of 21–17–2 in four years before Darrell Royal hired him in 1970.
McWilliams finished 7–5 in his first season at the helm for the Longhorns that included a dramatic last-play victory over the Arkansas Razorbacks and a bowl win over Pittsburgh.
Texas entered the New Year's Day Cotton Bowl Classic ranked number three in the nation, but was defeated by Miami, 46–3.
The resurgence gave rise to talk of a national title in 1991, but when Texas disappointed with a 5–6 record, McWilliams resigned.