Lackey, who spent his first eight seasons with the Angels, was signed to a five-year deal.
"It's always tough to make a change like this, but I'm really excited by it," Lackey said. "The Angels are all I've ever known."
While general manager Theo Epstein heard plenty this offseason about the need to obtain another bat, manager Terry Francona was constantly in his ear about getting another arm.
"Every time Theo asked me a question during the winter meetings, I would always say, 'A pitcher,'" said Francona. "Now we have a chance to run out a solid pitcher every day and it's very exciting. Again, it's on paper right now, but it will be our responsibility to go down to spring training and make it all work. But it's very exciting."
Francona gushed about having a top of the rotation that features a trio of aces in Lackey, Josh Beckett and Jon Lester. He's got plenty of depth at the back end as well in Tim Wakefield, Daisuke Matsuzaka and Clay Buchholz.
"It makes us all a lot smarter," Francona joked when asked about what Lackey's addition meant to Boston.
Cameron was signed to a two-year pact and was introduced at his own news conference two hours before Lackey's. Flanked by general manager Theo Epstein and manager Terry Francona, Cameron put on a No. 23 jersey and said one of the primary reasons he came to Boston was for the chance to win a World Series ring.
"It's a pretty special moment," Cameron said. "I haven't been this excited since I first came into the big leagues. This is a historical park ... hopefully I can put some dents in the Monster."
Primarily a center fielder during his 15-year career, there are questions about where exactly Cameron will play this season, but the trio indicated they needed to sit down as a group with incumbent center fielder Jacoby Ellsbury to discuss how roles will be assigned.
"I think what we need to do, and I've already talked to Cam about this, is, in the next week or so, I need to sit down with Theo, Mike, Jacoby, and probably DeMarlo [Hale] and figure out what is in our best interest," Francona said. "I need to talk to everyone first. It's been a whirlwind week for everyone, so we need to sit down and try to put the right pieces in the right place. I have some ideas, but I want to talk to everyone about it first."
Cameron, who turns 37 next month, batted .250 with 24 home runs and 70 RBIs last season for Milwaukee. A three-time Gold Glove winner in center field, he could switch to left with Boston as a replacement for free agent Jason Bay.
Cameron received a two-year contract that would be for a total of about $15.5 million, a source told ESPN.com's Jerry Crasnick.
The deal with Lackey, the top pitcher on the free-agent market after spending eight seasons with the Angels, is worth $82.5 million over five years.
The acquisition of the 31-year-old right-hander gives the Red Sox one of the best rotations in baseball. He is 102-71 with a 3.81 ERA in 234 career games.
Information from ESPNBoston.com's Chris Forsberg was used in this report. The Associated Press contributed to this report.