Burnett passed his Pirates physical on Sunday and Commissioner Bud Selig approved the transaction, a necessary step because of the money involved changing hands between the two clubs.
The Yankees will receive two Minor Leaguers in exchange for the 35-year-old Burnett -- right-handed reliever Diego Moreno, 25, and outfielder Exicardo Cayones, 20. Neither was considered among the Bucs' top prospects.
Pittsburgh will be responsible for paying $13 million of the remaining $33 million Burnett is owed through 2013, meaning the Yankees will ultimately cough up $20 million not to have Burnett pitching for them.
Burnett was viewed as an excess piece for the Yankees, who acquired Hiroki Kuroda and Michael Pineda this offseason while also re-signing Freddy Garcia.
Burnett's exit relieves that crunch, and the Yankees now figure to have six starters competing for five spots in their rotation, with Garcia and Phil Hughes battling for the final opening.
"Unfortunately, I've been around long enough to realize what appears to be a surplus can turn into a deficit rather quickly based on health," Yankees general manager Brian Cashman said.
In Burnett's case, however, the Yankees became motivated sellers after enduring back-to-back disappointing seasons of watching the inconsistent Burnett search for the form that saw him post 13 victories and help the Yankees win the 2009 World Series.
The two players received from Pittsburgh will report to the Yankees' Minor League camp this spring. Moreno is a power-armed reliever who had a 3.05 ERA in 17 Venezuelan Winter League appearances, pitching as high as Double-A Altoona last season.
He had fallen out of favor with the Pirates organization following a July 2010 suspension for an incident involving a female fan at Altoona and was not protected in December's Rule 5 Draft.
Cayones, a left-handed batter, hit .210 last season between the Class A Short-Season State College Spikes (New York-Penn League) and the Gulf Coast League Pirates.
The Yankees started shopping Burnett during the Winter Meetings in early December. Before reaching a deal with the Pirates, the Yankees also discussed moving Burnett to the Angels, Phillies and Indians, though talks never progressed far.
Despite Burnett's struggles on the diamond, he was generally regarded as a good teammate and became known for throwing whipped cream pies in players' faces after walk-off victories.
Yankees ace CC Sabathia said on Sunday that it was difficult to see Burnett leave, but he believes the move will be a positive one for Burnett.
"We came into this thing together, and it's just tough to see him go," Sabathia said. "But I think it's the best for him, and we just move on. It's part of the game, he's been around a long time, and I think he understands. Just a change of scenery, sometimes that does well for guys, and hopefully that can do well for him."
Burnett's Yankees career ends with a 34-35 record and a 4.79 ERA after signing a five-year, $82.5 million contract prior to the 2009 season. He was 11-11 with a 5.15 ERA in 33 games (32 starts) last year, and posted a 5.26 ERA in 2010.
While Burnett had some low moments -- slicing his palms after attacking a Yankee Stadium door in July 2010, pitching with an unexplained black eye in September 2010 and hints of a rift at times with manager Joe Girardi -- he was at his best in Game 2 of the 2009 World Series, when he struck out nine Phillies and outdueled Pedro Martinez to even the Fall Classic.
Without that victory, the Yankees would have headed to Philadelphia trailing the Phillies two games to none. Though Burnett faltered in a Game 5 start on short rest at Citizens Bank Park, the Yankees were in control of the Series by then and clinched in Game 6 at Yankee Stadium.
As Sabathia said, changing leagues and teams could help Burnett, who was hurt by homer-friendly Yankee Stadium -- a Major League-high 17 percent of the fly balls he surrendered cleared the walls -- as well as a dip in fastball velocity.
PNC Park figures to be a more forgiving workplace, and he continues to be a reliable strikeout pitcher (173 in 190 1/3 innings last year) despite losing a few ticks on his fastball. Burnett also should benefit from not seeing loaded AL East lineups on a regular basis.
Once the Yankees unload Burnett, they are expected to use part of their savings to delve deeper into the free-agent market for a designated hitter. New York has serious interest in veteran Raul Ibanez, and continues to entertain re-signing corner infielder Eric Chavez.
"We've got our hands full [in the AL East]," Cashman said. "That's why I hope and pray that what we've done this winter will help line us up to some degree."