The five-year extension is worth $55 million, with Atkins earning $22 million in the first six months, a person briefed on the deal told NFL.com's Ian Rapoport.
Geno, a fourth-round draft pick, was slated to earn $1.4 million in the last year of his rookie deal.
"It means a lot, just that they believed in me," Atkins said during a news conference. "... It shows young guys that do the right things on and off the field, and you will be rewarded, too. Now I can just kinda focus on football. ... I'm happy to play football and help the team go to the Super Bowl."
Atkins has become one of the NFL's biggest inside forces. The defensive tackle had 23 sacks in his first 48 NFL games, for a rate of .479 sacks per game, according to Randall Liu, the NFL's director of NFC football communications. By comparison, Hall of Fame defensive tackle Warren Sapp had a career rate of .487 sacks per game.
And, oh, how he got paid.