He missed the final 72 games and all seven playoff games during the 2007-08 season, and another 15 games during the 2008-09 season with the head injuries. There were some who questioned if he ever could return to being the kind of player who could help a team win a championship.
Well, he certainly proved he's all the way back in Game 7 of the Stanley Cup Final on Wednesday, scoring a pair of goals -- the game-opening goal in the first period and a shorthanded goal late in the second that gave the Bruins a 3-0 lead.
It capped a postseason that saw him finish second on the team in scoring with 20 points, but lead in so many other ways. He was a dominant defensive presence, was second in ice time per game among the team's forwards at 18:42, saw ample time on the power play and the penalty kill, and his 60.2-percent success rate in the faceoff circle was third-best in the postseason.
That's a far cry from the 2007-08 and 2008-09 seasons, when he played a total of 74 games.
"Obviously things always happen for a reason," Bergeron told NHL.com. "I think I've learned, I've grown from that. Yes, there was adversity, and I overcame it. To be honest, it's behind me. It made me the person I am today. I'm just so happy and I always believed that we could do it, that I could get back and do this.
"I never did (doubt he could come back). I always knew I was going to come back."
And he wanted that comeback to be with Boston, the team that drafted him in the second round of the 2003 Entry Draft (No. 45). He signed a three-year contract extension on the eve of the Bruins' opener in Prague, to avoid free agency this summer, so he'll have lots of time in the Hub of Hockey to enjoy his championship.
"I always believed Boston was the right city for me to get a championship," he said. "It's something I wanted to do. This is the team that drafted me and the team that believed in me. I wanted to do it."
Because of what he means to the team, Bergeron was the third player to carry the Cup, after captain Zdeno Chara and retiring veteran Mark Recchi. The handoff from Recchi was when Bergeron said he allowed all the emotion to bubble over.
"Getting it from Rex, that was something special in itself," said Bergeron. "And then getting the Cup was an amazing moment. Lots of relief, lots of stress, lots of memories, lots of emotions going through my mind. It was amazing.
"It was perfect. Exactly like I could dream of. It was perfect."
While the road to Stanley Cup glory hasn't been an easy one, Bergeron said lifting the Cup on Wednesday was that much sweeter because of the bumps along the way.
"After the injuries, I think it made me realize I had to appreciate every second of when I stepped on the ice and be thankful I had a chance to be back," he said. "I'm just happy."
Contact Adam Kimelman at email@example.com. Follow him on Twitter: @NHLAdamK