The 6-foot-11 Garnett had been sidelined for two games by a left thigh injury and the flu. Boston split the two games, losing to streaking Miami on in the final seconds Monday night.
Garnett is averaging 14.8 points and 7.8 rebounds this season.
His return comes as Boston attempts to climb into one of the top four playoff seeds in the Eastern Conference. The Celtics (36-30) entered Wednesday night's game only 2 1/2 games behind Brooklyn for the fourth spot, which guarantees home-court advantage in the playoffs for at least one round.