In fall 2005, Williams was hired by new head coach Nate McMillan as an assistant coach for the Portland Trail Blazers. On June 29, 2015, Williams became the associate head coach of the Oklahoma City Thunder. On June 1, 2016, it was announced that Williams would not return with the Thunder. On June 4, 2018, Brett Brown announced that Williams would join his staff in Philadelphia as the lead assistant coach, his first coaching job in two seasons. New Orleans Hornets/Pelicans On June 7, 2010, Williams was offered a three-year contract to be the head coach of the New Orleans Hornets. At the date of hiring, Williams became the youngest head coach in the NBA at 38 years old. In his first season with the Hornets, the team finished with a 46–36 record and made the playoffs. On August 18, 2012, Williams accepted a four-year contract extension from the Hornets (later renamed as the Pelicans). 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. On May 12, 2015, Williams was let go after five seasons as head coach of the Pelicans, compiling a 173–221 regular season record and going 2–8 in the playoffs. Phoenix Suns In May 2019, the Phoenix Suns announced they had signed Williams as the team's head coach on a five-year deal. The Suns compiled a 26–39 record in his first season coaching them before the season was postponed due to the COVID-19 pandemic. The Suns were later invited to the 2020 NBA Bubble in order to play eight seeding games, where Williams coached the Suns to an 8–0 record, improving their overall record that season to 34–39. Despite this, the Suns failed to qualify for the play-in tournament to enter the 2020 NBA playoffs. 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. After the conclusion of the 2020–21 season Williams was named NBCA Coach of the Year. He also finished second in the NBA Coach of the Year voting behind Tom Thibodeau. The Suns finished the season with