Oakland also was part of the nine-player swap. Money was a key factor, too. The Blue Jays sent $6 million to Philadelphia with Halladay, who then agreed to a $60 million, three-year contract extension through 2013.
"Without question, Roy is one of the top pitchers in the game today," Phillies general manager Ruben Amaro Jr. said in a statement. "He has the talent, professionalism and makeup that embody what we look for in players and we're very happy to have him in a Phillies uniform for at least the next four seasons."
Toronto sent Halladay to the Phillies for three minor leaguers: catcher Travis d'Arnaud, right-hander Kyle Drabek and outfielder Michael Taylor.
"This is where we wanted to be," Halladay said at Citizens Bank Park. "It was an easy decision for me. Once the opportunity came up for me to be part of this, it was something I couldn't pass up."
Halladay has never pitched in the postseason in his 12-year career with the Blue Jays. He coveted the chance to play for the 2008 World Series champs, hoping for an opportunity to win his own ring.
"I think the older you get, the longer you play in your career, the more important that becomes," Halladay said. "The more I play, the more I realize how important that is to me."
Halladay received a standing ovation when he was introduced at Wednesday night's 76ers game. He waved to the nearly 20,000 fans from his suite.
Halladay has an offseason home near the Phillies' spring-training complex in Clearwater, Fla.
Toronto sent the 32-year-old Halladay to Phillies for three minor leaguers: catcher Travis d'Arnaud, right-hander Kyle Drabek and outfielder Michael Taylor. The Blue Jays flipped Taylor to the Athletics for third baseman Brett Wallace.
"We weren't sitting back and seeing what was offered. We asked for specific players and were trying to get the best value that we could and that's why we explored a lot of three-, four-, five-team deals," Toronto general manager Alex Anthopoulos said.
The Phillies dealt Lee to Seattle for three prospects: right-hander Phillippe Aumont, outfielder Tyson Gillies and right-hander Juan Ramirez.
The Phillies actively pursued Halladay at the trade deadline, but balked at parting with lefty J.A. Happ. The Phillies could have made this deal with Toronto and kept Lee to form a formidable 1-2 Cy Young punch at the top of the rotation.
"If I had my druthers, I'd love to have both of them on the club," Phillies general manager Ruben Amaro Jr. said.
Amaro said he didn't keep Lee, who has one year and $9 million remaining on his contract, for two reasons. He felt Lee wanted to test the free-agent market next winter and couldn't afford to keep him and lose him for nothing. And he needed prospects to replenish the ones lost in both the Lee-from-Cleveland trade and the Halladay deal.
"I had a little discomfort that we'd be able to do the type of deal that I'd feel comfortable with," Amaro said.
Halladay had been prominently mentioned in trade talk since the All-Star break. The five-month talks ended when all sides signed off on the deal.
Halladay went 17-10 with a 2.79 ERA last season. The righty led the AL with four shutouts and nine complete games. The six-time All-Star won the 2003 AL Cy Young.
"I'd hate to play my career based on where you get the most years," he said. "I want to do it for what I believe are the right reasons. All the right reasons are here."
The deal began building in talks with new Toronto GM Alex Anthopoulos months ago. Mariners general manager Jack Zduriencik spoke to Amaro at last week's winter meetings -- and even in the Indianapolis airport as both GMs were leaving town.
Zduriencik's interest peaked when Amaro, who had pushed hard to get Halladay last summer, asked Seattle's GM, "If I'm able to do Halladay, would you be interested in having Cliff Lee?"
Zduriencik's answer was something akin to "Duh!"
"When you have the opportunity to acquire a pitcher of Cliff's caliber, immediate effects are (obvious)," Zduriencik said. "Did I think we'd be getting a guy of this caliber? You always set your expectations high. We're really glad it came to fruition."
Lee was the reigning AL Cy Young Award winner when the Phillies got him from Cleveland last July 29. The 31-year-old lefty went 7-4 with a 3.39 ERA down the stretch, then excelled in the postseason by going 4-0 with a 1.56 ERA in five starts.
Lee earned both of the Phillies' wins in the World Series against the New York Yankees.
Halladay will make $15.75 million next year. The amount of cash the Phillies got from Toronto almost covers the difference in the salaries for Halladay and Lee.
Halladay's extension pays $20 million annually from 2011-13. There is a $20 million option for 2014 that becomes guaranteed if he meets all three of the following: pitches 225 innings in 2013, pitches 415 innings combined in 2012 and 2013 and is not on the disabled list at the end of the 2013 season.
"If we had just acquired Roy and not moved Lee, we would have been in position to have lost seven of the best 10 prospects in our organization," Amaro said. "That is not the way you do business in baseball."
Gillies, 21, hit .341 last season and led the California League with 44 stolen bases at Single-A High Desert. He scored 104 runs and had a .430 on-base percentage.
Aumont, 20, went a combined 2-6 with 16 saves and a 3.88 ERA for High Desert and Double-A West Tennessee last season. A first-round draft pick in 2007, he pitched for Canada in the 2009 World Baseball Classic.
Ramirez, 21, was 8-10 with a 5.12 ERA for High Desert.
Drabek, 22, was a combined 12-3 with a 3.19 ERA at Single-A Clearwater and Double-A Reading. He was the Phillies' first-round draft pick in 2006 and his father is former NL Cy Young winner Doug Drabek.
D'Arnaud, 20, hit .255 with 13 home runs and 71 RBIs at Single-A Lakewood.
Wallace was acquired by Oakland last season as part of the trade for Matt Holliday. At 23, Wallace hit a combined .293 with 20 home runs and 63 RBIs for three teams.
Taylor, 23, hit a combined .320 with 20 home runs, 84 RBIs and 21 stolen bases at Double-A Reading and Triple-A Lehigh Valley. He joined a relatively small group of players who have been traded twice in one day. His stay with Toronto wasn't long.
"It was all of 38 minutes I believe," he said.
Information from The Associated Press was used in this report.