Casey joined the NBA ranks as assistant coach for the Seattle SuperSonics from 1994 to 2005. He got his first NBA head coaching job with the Minnesota Timberwolves from 2005 to 2007. From 2008 to 2011 Casey was an assistant coach for the Dallas Mavericks and in 2011 he became head coach of the Toronto Raptors. As an assistant he won an NBA Championship with the Mavericks in 2011. In his last contract with the Raptors, Casey was earning $6 million per year. He was fired in May 2018 after getting shut out in the playoffs by the Cleveland Cavaliers.