Williams, widely projected to be a first-round pick in the draft, is ranked No. 16 overall on ESPN's Mel Kiper Jr.'s most recent Big Board. He will also sit out the Longhorns' bowl game in preparation for the draft.
"I consider myself extremely fortunate to have spent the past three years at the University of Texas," Williams said in a statement. "The array of emotions and experiences through my years on the 40 Acres has been nothing short of amazing."
Williams was a preseason Associated Press All-American and started five games for Texas this season, missing seven because of a knee injury that required surgery. He started 28 games in his Longhorn career.
The Longhorns are going to a to-be-determined bowl game for the first time since 2013.