Justin Williams (born May 12, 1984) is an American former professional basketball player. He is a 6 ft 10 in (2.08 m), 260 pounds (120 kg) power forward-center.

Born in Chicago, Illinois, Williams attended Thornwood High School, in South Holland, Illinois, where he played high school basketball.

Williams played college basketball the Colby Community College, from 2002 to 2004, and at the University of Wyoming, with the Wyoming Cowboys, from 2004 to 2006.

Williams went undrafted by an NBA team and started to play with the NBA Development League's Dakota Wizards, averaging 12.1 points, 12.3 rebounds and 3.08 blocks in 12 games. He was signed by the Sacramento Kings to a first 10-day contract on January 5, 2007. After the Kings released power forward Maurice Taylor on January 23, Williams was signed for the rest of season after his two 10-day contracts expired.

On February 16, 2008, Williams was waived by Sacramento together with teammate Dahntay Jones to make room for a trade that sent the Kings' veteran point guard Mike Bibby to the Atlanta Hawks. On March 7, he was signed by the Houston Rockets to a 10-day contract. He played in one game for the Rockets.

Williams was brought to Golden State Warriors training camp on September 27, 2008, but he was cut after appearing in two pre-season games.

On October 16, 2008, Williams was signed by the Charlotte Bobcats. But six days later, he was waived again after failing to impress in three pre-season games.

In 2012, Williams signed with the Los Angeles D-Fenders of the NBA D-League. He played in one game for the D-Fenders recording just one foul in two minutes of play.