The Celtics also announced Saturday that forward Brandon Bass and center-forward Chris Wilcox have signed to remain with the team that made it to the Eastern Conference finals - where it lost in seven games to eventual NBA champion Miami.
Garnett had an outstanding season, especially down the stretch and in the playoffs. He averaged 15.8 points, 8.2 rebounds and 2.9 assists in his fifth season with Boston.
Bass averaged 12.5 points and 6.2 rebounds after being obtained from Orlando. Wilcox, also in his first season with the Celtics, had surgery for an enlarged aorta after playing 28 games, averaging 5.4 points and 4.4 rebounds.