Chara, who logged a total of 26 minutes and 20 seconds of ice time, assisted on Nathan Horton's first-period goal as the Bruins prevailed 4-2 to cut Montreal's series lead to 2-1.
"I felt good," Chara said.
He added: "I wasn't feeling well and I tried to play [Saturday] but we decided not to. It took me another 24 hours to recover. Since this morning I knew it was likely I could play."
Chara missed Game 2 due to dehydration. The 6-foot-9 defenseman defenseman participated in Monday morning's game-day skate, but the team wanted to give him the entire day, including the pregame warmup, before making a final decision whether or not he would play.
"He's arguably the strongest guy in the league and he's not easy to play against," Bruins coach Claude Julien said. "Whenever you take him out of the lineup, you're taking a big piece out of there. Tonight we were glad to have him back. We were gauging his game by how he was going to be feeling period after period and he seemed to feel good. We kept giving him the ice time he was capable of handling."
Chara's teammates knew having him back would add a spark.
"He makes a huge difference," said goaltender Tim Thomas. "He's one of the most important players if not the most important players on this team and one of the best defensemen in the league and it's harder to play without him. Last game we all wanted to step up for him and we weren't able to get it done but it was nice to see him back and he's such a big part of our team."
Meanwhile, Montreal Canadiens winger Andrei Kostitsyn also returned after missing Game 2 with a foot injury. Kostitsyn, who was skating on the right wing with center Tomas Plekanec and Mike Cammalleri, scored a goal in the assist.
Kostitsyn was injured while blocking Chara's shot in Game 1.
Forward Jeff Halpern, who hadn't suited up since late in the regular season, did not return for Montreal. Halpern has been skating with the team for a week.
Chara missed Game 2 on Saturday in Boston with what the team described as dehydration after spending last Friday in the hospital. Prior to that game it was decided that he would attempt to play, but he took a turn for the worse during the pregame skate and the team decided to keep him out of the lineup, according to a team source.
Chara's return Monday also marked his first game at the Bell Centre since his check on Canadiens' Max Pacioretty that resulted in the forward suffering head and neck injuries.
Montreal police are currently conducting a criminal probe into the matter. The Bruins are not concerned with the fans in Montreal being a distraction for Chara.
"That doesn't matter," Julien said before the game. "What matters to us right now is what's at stake and that's the game. No matter what happens you have to play through those things and we're all aware of that. Guys are professionals enough and I don't know if there's a rink where Zdeno doesn't get booed in.
"It's certainly not because of what happened, but because the realization of the impact that he has on the game and the difference he can make. In a game situation, he's a big man. He's a big strong guy that we rely on a lot. He's a big part of our team and I think other buildings realize that."
Joe McDonald covers the Bruins for ESPNBoston.com. Information from The Associated Press was used in this report.