On December 21, 2011, he signed a two-year contract with the Dallas Mavericks. The Mavericks then assigned him to the Texas Legends of the D-League. Williams played his first game for the Mavericks in their 115–93 loss to the Denver Nuggets on December 26, 2011, providing some much needed spark off the bench in the 3rd quarter. Williams went 4–4 from the field, which included two high flying alley-oops, and 4–4 from the free throw line and picked up 3 rebounds, a steal and a block in his 11 minutes of game time. As he was leaving the court in the fourth quarter, he threw up on the Mavericks bench.