Mason, a 2015 fourth-round draft choice out of Georgia Tech, will receive $23.5 million in bonuses and guarantees as part of the deal. That total includes the $1.9 million base salary he was scheduled to earn in 2018.
Of the $50 million pact, a total of $5 million is tied to incentives and honors. Mason, who turns 25 on Tuesday, was scheduled to become an unrestricted free agent after the 2018 season.
While head coach Bill Belichick didn't confirm the extension on Monday, he acknowledged that Mason has improved each season.
"Shaq has done a good job for us from the time he got here," Belichick said. "He came from an [option-based] offense that was quite different from ours and he adapted quickly. He did a real good job of learning new techniques. He's an athletic player and has good strength, good balance, an excellent run-blocker. He can pull, run and hit."
The 6-foot-1, 310-pound Mason, who often tweets that he's "thankful for another 24," has played in 46 regular-season games for the Patriots, with 41 starts. He's also started eight postseason games.
His full name is Shaquille Olajuwon Mason, given to him by his mother as an ode to former NBA greats Shaquille O'Neal and Hakeem Olajuwon.
The guard financial market has exploded in the past year, led by Zack Martin of the Dallas Cowboys, who signed an extension worth $14 million per season, and Andrew Norwell or the Jacksonville Jaguars, who inked a free-agent deal worth $13.3 million per season.
NFL Network first reported news of Mason's extension.