On June 28, 2007, Green was selected with the fifth overall pick in the 2007 NBA draft by the Boston Celtics. He was later traded to the Seattle SuperSonics alongside Wally Szczerbiak and Delonte West in exchange for Ray Allen and Glen Davis. On April 6, 2008, Green scored a career-high 35 points against the Denver Nuggets. Green made the NBA All-Rookie First Team in 2008 after averaging 10.5 points, 4.7 rebounds and 1.5 assists in 80 games.
On December 10, 2011, following the conclusion of the NBA lockout, Green re-signed with the Celtics.Eight days later, his contract was voided by the Celtics after a routine physical examination detected an aortic aneurysm. He subsequently underwent heart surgery in January 2012 and missed the entire 2011–12 season.On July 10, 2018, Green signed with the Washington Wizards.
