The team didn't disclose terms, but sources told ESPN the deal is worth $13 million with $6 million guaranteed.
Celek's previous contract was set to expire after the 2016 season, but he's now signed through 2018.
Celek, a fifth-round pick in 2007, worked his way up the depth chart at tight end over his first two seasons and wound up being a full-time starter in his third year.
While Celek was known for his pass-catching abilities earlier in his career, he wound up becoming one of the best blocking tight ends in the NFL in recent seasons.
The expectation around the NFL is that under new head coach Doug Pederson, the tight end position will become an even bigger part of the team's passing game.