Lowry and P.J. Tucker were both in the starting lineup announced by Miami shortly before tipoff.
Lowry has not played since reinjuring his left hamstring in Game 4 of the East semifinals series against the Philadelphia 76ers. Tucker left Game 2 of the Boston series with a knee contusion.
Meanwhile, Celtics center Robert Williams III will miss Saturday's game as he continues to deal with a left knee issue, the team announced.
Celtics coach Ime Udoka said Williams has soreness and swelling in the knee. He missed three games of the Celtics' East semifinals against Milwaukee before returning in Game 7 to help Boston close out the Bucks, and he had played the first two games against the Heat.
Lowry initially suffered the injury in Game 3 of Miami's first-round series against the Atlanta Hawks. He missed the last two games of that series and the first two of the Sixers series before trying to return.
Lowry's return should provide an emotional lift for a Heat team that comes into Game 3 tied at 1-1 with the Celtics -- but having gotten dominated by Boston in a 127-102 Game 2 loss in Miami. Heat players and coaches have mentioned many times how helpful Lowry's presence has been on and off the floor -- and his return has the attention of a strong Celtics team, as well.
"Kyle brings shooting, he brings intensity when it comes to the defensive end," Celtics forward Grant Williams said after the Saturday shootaround. "He uses his body in great position; you don't necessarily want to post him up, he does a great job taking charges, kind of flailing, getting the referees into the game.
"He's a vet that you have to take out of the game because he provides a scoring push for them, as well, and they play a lot more in transition when he plays. He kicks the ball ahead, he's willing to pull up in transition 3s, flying off of actions. So it gives them a different dynamic. It's going to be fun to have him back because you want every team to be fully healthy so you can compete at the highest level, and hopefully P.J.'s knee is good too, so we all can kind of go out there and kind of play our best game of basketball."
ESPN's Tim Bontemps contributed to this report.