Herro made his first appearance early in the second quarter, checking in to a standing ovation.
Herro has been out over a week since suffering a left groin strain in Game 3 on May 21. Herro spent some time getting shots up and trying to stay loose before the biggest game of Miami's season.
"Right now it's all hands on deck," Heat coach Erik Spoelstra said during his pregame availability. "He passed his testing with the trainers. He's really been working diligently the last few days. Each day he's made significant improvement, and he was able to do shootaround this morning, but more importantly he was able to do things in the training room and pass those tests to be available."
Herro averaged 12.3 points, 3.7 rebounds and three assists over the first three games of the series.
For the Celtics, Defensive Player of the Year Marcus Smart and center Robert Williams III both started and were without any minutes restrictions. They were originally listed as questionable for the series finale.
Smart has been dealing with an ankle sprain, and Williams is playing through ongoing knee soreness following surgery.
The Associated Press contributed to this report.