Williams, a 5-foot-9, 200-pound junior from Houston, rushed for 1,760 yards with 18 touchdowns on 271 attempts in 13 games.
"I have decided that it will be best for me and my future to forgo my senior season and enter the NFL draft," Williams said in the video.
Williams is ranked the No. 6 draft-eligible running back by ESPN's Mel Kiper Jr.
Williams helped lead the Aggies to a 9-4 record in coach Jimbo Fisher's first season. He averaged 6.5 yards per carry and 135.4 yards per game, which was tops in the SEC.
Williams ran for more than 100 yards in nine games and more than 200 in three. He had 236 yards with three touchdowns in the Aggies' 52-13 victory over NC State in the TaxSlayer Gator Bowl.