McCoy, a 2013 All-Pro, will get $51.5 million guaranteed, the most ever given to a defensive tackle in NFL history.
League sources told ESPN's Chris Mortensen that the extension is worth $95.2 million, and could reach $98 million with escalator clauses. He will average $13.6 million per year, and $14 million annually if those escalators kick in.
McCoy's signing was reported earlier Saturday by Fox Sports. The Buccaneers confirmed the deal and posted a photo of McCoy shaking hands with general manager Jason Licht on their official Twitter page.
McCoy was making $13 million this year and part of it was a $7 million roster bonus, so he will pocket $20 million for 2014.
He entered league under the former collective bargaining agreement, so his franchise tag value would have been estimated at $18 million in 2015 and $25 million in '16.
The deal was concluded Saturday by Licht and McCoy's agent, Ben Dogra.
"Gerald is extremely excited to remain with the Tampa Bay Buccaneers and he is especially thankful to Bucs owners, coaches, and Jason Licht for working so hard throughout the process," Dogra said.
McCoy is in his fifth NFL season and comes off his best year, when he had 9.5 sacks and 35 tackles. He is considered the anchor of Tampa Bay's rebuilding defense.
The Buccaneers (1-5) have struggled this year, allowing a league-high 204 points. But McCoy is among the league's best defensive tackles, often drawing double teams. He has played part of this season with a cast on his broken left hand.
Now, McCoy has long-term security in Tampa and can begin working on getting the Bucs into the postseason, something he has never experienced.
"That's eating away at me, man," the 6-foot-4, 300-pound McCoy said this summer. "I do all this training and preparing, trying to do what I can for my team for us to get to the playoffs. I just want to experience it."
ESPN's Chris Mortensen and The Associated Press contributed to this report.