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 his 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.