An impressive postseason showing against the B's in the '09 conference semifinal solidified his reliability, and in March 2010, when the hard-nosed blueliner - then, a Florida Panther - became available at the trade deadline, Chiarelli made his move. The Bruins acquired Seidenberg and Matt Bartkowski in the trade with Florida.
With an expiring contract, Chiarelli locked him up during the 2010 offseason.
And if anything, Seidenberg has only improved since finding a home - and a Stanley Cup - with Boston.
On October 3, the defenseman signed his second four-year contract extension with the Bruins, that keeps him in Black & Gold until at least the 2017-18 season.
"Everything took off here," Seidenberg said, after inking the extension (and helping the Bruins win their season opener over Tampa Bay).
"Everything started, basically, here. I finally found a spot where things worked out the way I’d always imagined. So that’s fun. I’m very happy that it worked out."
The German Hammer's heavy game has weighted down the back end for the Bruins since his arrival, and his unsung playoff hero status (usually forming the team's top shutdown pair with Zdeno Chara) has powered them to the Stanley Cup Final in two of the last three seasons.
I finally found a spot where things worked out the way I’d always imagined - Dennis Seidenberg
On the way to the Cup, he skated in all 25 games, proving to be an unsung hero much like this past 2013 postseason. As a Bruin, he's played in 50 playoff games, tallying two goals and 13 assists. But being offensive-minded is never his first priority.
A shot-blocking machine and heavy-minutes logger, Seidenberg often paves the way for the B's throughout the regular season and playoffs by thwarting others' paths.
"You don’t hear about him that much, but all the little things he does out there goes a long way, especially at this time of the year," alternate captain Patrice Bergeron had said during the 2013 playoffs. "We recognize it in this room and I’m sure that’s all that matters to him."
His workhorse mentality is also dually noted by his general manager.
"Dennis has been in the league a while. The year before we made that trade, you heard me say around when we made that trade about his hockey sense improving, and it's only improved since he's been with us," Chiarelli said, as he addressed media regarding the extension on October 3.
"He just, he clears pucks on the wall, that's hard, you have to be strong. You saw him in that series against us [in 2009], and the whole playoff year that year and then with us - he plays like a fullback but with the skills to clear the puck too."
"He clears the lane, he's a really really strong, strong player. Again, hard to find those guys. Hard to find the guys with strength like that, that can clear pucks like that and still make plays."
Seidenberg found his fit in Boston. He came into the 2013-14 season having played 224 games as a Bruin, just under half of his 581 career NHL games, with 18 goals, 63 assists and a plus-45 rating since joining the team in March 2010.
Now, he's considered a key cog in the strong veteran leadership group.
"He's been one of our core guys since we got him. You hear me talk often about character guys; he's definitely that on and off the ice," said Chiarelli. "He's been a warrior for us."
"There's a lot of things that he has that are compatible with the way we want to play."
For Seidenberg, being counted on and trusted with his role has given him immense pride in wearing the spoked-B while doing so.
"I take a lot of responsibility in working hard every game and just doing my job – playing hard minutes, playing tough defensively, and just winning my one-on-one battles," said the defenseman, reacting to Chiarelli labeling him a "warrior" for this team.
"It’s nice to hear when somebody says something like that."
Part of Seidenberg's warrior status is his elite fitness level, allowing him to log the workhorse minutes like Chara. He's the type of player who may receive a penalty that you could look at and say: 'two minutes for being strong.'
"D like Dennis are hard to find. I think he's been so good for us and the way that he plays is hard to find," said Chiarelli. "We've got D in the depth of the pipeline that have bits and pieces of their game who play like that but not the whole package. So I felt he's in super condition - knock on wood, he's very rarely been injured - and he plays heavy, heavy minutes."
D like Dennis are hard to find. I think he's been so good for us and the way that he plays is hard to find - GM Peter Chiarelli
Logging anywhere from 20 to 30 minutes per game, Seidenberg averaged 23:48 in ice time throughout the 2012-13 season.
"He's 32 but we feel he's in good condition, he takes care of himself and he wanted to stay here, so it was easier to get done," Chiarelli said of the ease of the deal, which still always involves some give and take on both sides.
"He does play hard but the way he takes care of his body, he’s going to get bumps and bruises along the way but we felt to have him around for a long period of time, four years, was feasible."
The first two and a half years of the deal involve a full no-trade clause, followed by a partial no-trade clause for the remaining time.
"I’m at a stage where I’ve got to look at my family, I mean, I’ve got kids in school now and you want to kind of plan and know what’s going on next year so that’s why I wanted to get it over with," said Seidenberg, of getting it wrapped up before the season, so he could just concentrate on his performance.
After 2013-14 - the final year of his current deal before the extension kicks in - he could have gone to the free market.
"At the end of the day we wanted to keep him, Dennis wanted to stay here, and you’ve heard me say this before – he probably gave up some money," said Chiarelli, of the negotiations.
"I have a lot of fun playing here, and that’s important, and the coaches have trust in me and that’s the most important thing," Seidenberg remarked. "If I go somewhere else for a lot of money and then things don’t work out that way, I think to be honest, in this situation, [staying here] was the most important part. We have a good team here and in the future I think we’re going to be good for a lot of years."
"Peter is doing a great job of securing a lot of our core group and Seids has been a real solid player for us," added Head Coach Claude Julien, of his trustworthy D-man.
"He does all the things that a strong, hard-nosed defenseman has to do. He’s pretty durable and reliable, so it’s nice to have those guys signed for longer terms."
"It just gives us some stability and I think, if anything, he certainly deserves it for what he’s done for us since he’s been here."