A league source told ESPN's Adam Caplan that the deal, which kicks in beginning in 2018, is for six years and $56.4 million, with $28.2 million guaranteed.
Frederick has yet to sign the contract. He was in the locker room getting dressed for Saturday's preseason game against the Los Angeles Rams when the deal became finalized.
"Obviously there's risk involved any time you step out on the field, whether it's practice or a game, so to have the security of having it done before I stepped on the field in case anything happened was important," Frederick said. "But also because I wanted to have that behind me so I could really focus on football."
The Cowboys drafted Frederick in the first round of the 2013 draft and he has not missed a start. He has been named to the Pro Bowl the past two years and is widely considered one of the best centers in the NFL.
The Cowboys were criticized when they took Frederick after moving down to the 31st overall pick in a deal with the San Francisco 49ers. They also acquired a third-round pick in that trade that turned into wide receiver Terrance Williams.
In the spring, the Cowboys picked up the fifth-year option on Frederick's rookie deal for 2017, guaranteeing him $8.8 million.
Talks with Frederick's agent, Joe Panos, picked up in earnest last week when he visited the Cowboys at their Oxnard, California, training camp facility. Panos also represents left tackle Tyron Smith, who signed an eight-year extension worth $98 million in 2014.
The Cowboys have made keeping their offensive line intact for years to come. It started with Smith in 2014, continued now with the deal for Frederick. Their 2014 first-round pick, Zack Martin, is eligible to sign a contract extension next year.
The NFL Network first reported the deal between the Cowboys and Frederick.