The deal, which runs through 2024, includes a $20 million signing bonus, a source told ESPN.
Martin skipped organized team activities without the security of the long-term contract, but he has attended the first two days of mandatory minicamp after progress was made last weekend in the negotiations.
The Cowboys had hoped to lock down Martin to a long-term deal during training camp last year, but the talks never ventured very far. Once the season began, Martin put the negotiations on hold but said he never wanted to leave the Cowboys. The talks began anew early in the offseason and the sides were close to a deal about a month ago before hitting a snag.
Those issues were resolved in the past few days.
The deal will make Martin the highest-paid guard in the NFL and among the highest-paid offensive linemen.
The Jacksonville Jaguars signed Andrew Norwell to a deal as a free agent earlier in the offseason averaging $13.3 million per season. He received a five-year, $66.5 million deal that included a $15 million signing bonus and $30 million guaranteed. In 2017, the Cleveland Browns signed Kevin Zeitler as a free agent to a five-year, $60 million deal that had $31.5 million guaranteed. The New York Giants signed left tackle Nate Solder to a four-year deal this year, averaging $15.5 million a year and with $34.8 million guaranteed.
Martin was set to count $9.341 million against the cap in 2018 as a result of the fifth-year option the Cowboys picked up last year. With the extension, the Cowboys will save some cap space this season and have comfort in knowing they have locked up their third Pro Bowl offensive lineman to a long-term deal.
The Cowboys took Martin in the first round of the 2014 draft (No. 16 overall), famously passing over Texas A&M quarterback and Jerry Jones favorite Johnny Manziel. Martin has not missed a game in his career, has been named to the Pro Bowl all four seasons, and has been named a first-team All-Pro twice and a second-team pick twice.
With Martin locked up, the Cowboys can turn their attention to defensive end DeMarcus Lawrence, who had a career-high 14.5 sacks in 2017. He is set to play the season on the $17.143 million franchise tag, but the team has until July 16 to work out a long-term deal.
Executive vice president Stephen Jones said recently that there are no negotiations on the calendar with Lawrence's agent, David Canter, but he hopes a deal can be worked out before the deadline.