In college, Williamson was a dominating power forward but became an undersized power forward in the NBA and has mostly played down at the small forward position.

He attended the University of Arkansas and in 1994 was named Most Outstanding Player of the NCAA Tournament while helping the Razorbacks win the NCAA Basketball Championship under coach Nolan Richardson.

He was selected by the Sacramento Kings as a 13th overall pick in the first round of the 1995 NBA Draft.

His best career year was in the 1997-98 season when he played 79 games and averaged 17.7 points per game for the Kings. After Sacramento traded him mid-way through the 2000-01 season to the Toronto Raptors (in exchange for Doug Christie), for whom he played 42 games, Williamson was traded to the Detroit Pistons where in the 2001-02 season he was named the NBA's Sixth Man of the Year and eventually was a member of the Pistons' 2003-04 NBA Championship team. After being traded by the Pistons along with an undisclosed amount of cash to the Philadelphia 76ers for Derrick Coleman and Amal McCaskill on August 8, 2004, he was again traded back to the Kings along with Brian Skinner and Kenny Thomas for power forward Chris Webber on February 22, 2005.

Williamson has gained certain fame for being one of the few Professional basketball players to win National Championships at three different levels, High School, the NCAA with Arkansas, and the NBA with Detroit.