Seguin, who was selected with the No. 2 pick in the 2010 Entry Draft and was a smash hit at the Bruins' development camp in July, agreed to a three-year entry-level contract with the team Tuesday.
"These deals aren't overly difficult to do," Bruins GM Peter Chiarelli said during a conference call to announce the signing. "There's some nuances to them, but there's a body of work on the No. 2 picks who have signed prior, and we felt it was time to sign Tyler. He's obviously a high pick and performed well in our development camp, and we thought it was time to sign him to give him peace of mind and make him feel part of the organization."
Seguin, a 6-foot-1, 172-pound center, played the past two seasons with the Plymouth Whalers in the Ontario Hockey League. Seguin and No. 1 draft choice Taylor Hall finished in a dead heat for the OHL regular-season scoring title with 106 points apiece last season.
Hall signed a three-year entry-level contract with Edmonton on July 5. He had 40 goals in 57 games, while Seguin produced 48 goals in 63 games. It marked the third time in the league's 76-year history that the scoring race was shared. The first stalemate occurred in 1971-72 when Toronto's Dave Gardner tied teammate Bill Harris with 129 points.
Seguin was in Wilmington, Mass., last month for Boston's development camp, where fans chanted his name every day when the Bruins' prospects took the ice and seemingly whenever Seguin touched the puck.
"I was surprised, and was like 'Wow! This is a big crowd,'" Seguin said at the time. "It just shows this is a good market and there's a lot of support here and the fans are great. Usually if anyone's talking about me it's like 'Seguini' or 'Seegin' or something. These guys, they have it right on point."
It's expected Seguin will have every opportunity during training camp to claim a roster spot and start the season in Boston, but Chiarelli didn't want to put any pressure on the young player.
"Nothing really has changed to make me more comfortable or not from where I last saw him," Chiarelli said. "He's a terrific young player, so I think he'll open some eyes at camp, but let's wait and see."
And assuming Seguin does make the opening night roster, he won't necessarily be playing his natural position.
"Right now I'd say he'd be on the wing, but you never know, things may change," Chiarelli said. "But we have four centermen with (David Krejci), (Patrice Bergeron), (Marc Savard) and Greg Campbell, so unless we ice another ceneterman, he'd be on the wing right now … but I can't tell you with complete certainty where he'd play."
Seguin was not part of Tuesday's conference call, but upon being drafted he was asked who he was most looking forward to playing with in Boston.
"Actually I just ran into Mark Recchi at the hotel a couple times," Seguin said. "He's going to give me a lot of advice, and I'm looking forward to that. And of course, I've seen (Zdeno) Chara play. He was probably the best player I've ever seen on the Bruins this past year, and I think it's going to be quite tough going one-on-one against him if I get that opportunity."
His most inspirational player growing up was Hall of Famer and current Tampa Bay GM Steve Yzerman.
"Steve Yzerman, he's always been my idol growing up," Seguin said. "Just the way he was on the ice, he started off as a rookie and had to mature as a player like I did. Getting better in the zone and stuff like that. And he turned into an all-around good guy. He's phenomenal off the ice and a true leader. Something that I want to be like myself."
NHL.com Correspondent James Murphy contributed to this report.