Terms were not disclosed but a source told ESPN's Adam Schefter that the deal is worth $9 million.
Pouncey started 16 games for the Chargers last season and earned his fourth Pro Bowl selection.
"From Day 1, Mike has been everything we thought he'd be and more," general manager Tom Telesco said in a statement. "He's an unquestioned leader, both in the locker room and on the field, who has earned the respect of teammates and coaches alike. His relentless work ethic -- there have been times where we've had to fight to keep him off the practice field -- and toughness are contagious. Mike's dependability is invaluable, and we're excited to have secured our Pro Bowl center through the 2020 season."
The 30-year-old is known for his strength as a run-blocker. He was a big factor in the Chargers' success in transforming into a physical running team last season.
Pouncey signed a two-year, $15 million deal with the Chargers in 2018 after being released by the Miami Dolphins because he refused to take a pay cut.
There were some concerns about his ability to stay healthy after the hip surgery he had two years ago. But Pouncey didn't miss a single game.
Pouncey's twin brother, Maurkice, is the starting center for the Pittsburgh Steelers.