He served as an assistant coach with the United States national team under Mike Krzyzewski, and he has worked as a vice president of basketball operations for the San Antonio Spurs.

As a 6 ft 8 in (2.03 m) small forward from the University of Notre Dame, Williams was an honorable mention All-American, averaging 22.4 points and 8.4 rebounds during his senior season.

[1] Williams was an NBA first-round pick despite a pre-existing heart condition that kept him out for two seasons at Notre Dame.

Williams was traded alongside Charles Smith to the San Antonio Spurs for Brad Lohaus, J.R. Reid and a future first round pick that became John Wallace.

[7][8] In spring 2005, Williams won an NBA championship as a coaching staff intern with the San Antonio Spurs.

[10] On June 7, 2010, Williams was offered a three-year contract to be the head coach of the New Orleans Hornets.

[13] On June 9, 2013, Williams accepted an assistant coach role with the U.S. national team, along with Jim Boeheim and Tom Thibodeau, for the 2016 Summer Olympics in Rio de Janeiro, Brazil.

The New Orleans Pelicans finished the 2014–15 season with a 45–37 record before losing to the Golden State Warriors in the first round of the playoffs.

[17] In May 2019, the Phoenix Suns announced they had signed Williams as the team's head coach on a five-year deal.

On November 16, 2020, Williams reunited with star point guard Chris Paul after last coaching him back in 2011 when they were with the New Orleans Hornets.

[24][25] Williams coached the Suns to a first round series victory over the defending champion Los Angeles Lakers in six games, and a sweep of the Denver Nuggets in the conference semifinals.

On January 30, 2022, Williams was named as the Western Conference head coach for the 2022 NBA All-Star Game as a result of his team's NBA-best record at 40–9.

[34] On May 13, 2023, the Suns fired Williams after losing to the eventual champion Denver Nuggets in the Western Conference semifinals of the 2023 NBA playoffs.

[36][37] During Williams' first year as head coach for the Pistons, the team lost 28 straight games, the longest losing streak within one season in NBA history.