The team announced the move Thursday.
McGuire appeared in 52 games with the Charlotte Bobcats last season, averaging 3.3 points and 3.8 rebounds in 14.6 minutes per contest. In eight starts, the 6-foot-9 forward averaged 3.8 points and 7.4 rebounds in 26 minutes per game.
McGuire was selected by the Washington Wizards with the 47th overall pick in 2007 out of Fresno State. He also spent two seasons at California.
The Warriors open the preseason at home against the Sacramento Kings on Saturday night.