Williams rushed for 1,140 yards on 157 carries with 19 touchdowns this season. He made history with teammate Michael Carter earlier this month as the pair combined for 544 rushing yards against Miami -- an NCAA record for two teammates.
"I would like to thank God for blessing me with the health and ability to play the game I love and allowing me to be in this position," Williams said in his announcement. "Thank you Coach Brown and the staff for giving me countless opportunities to display my talents."
Williams is ranked as the No. 3 running back on ESPN' Mel Kiper Jr.'s latest Big Board.
Carter announced on Monday that he would also forgo UNC's bowl game and enter the draft.