The Lions on Friday announced the extension, which ties Ragnow to the franchise through the 2026 season, but did not disclose the value of the deal.
"When you sign a contract like this, it's kind of hard to digest that amount of money," an emotional Ragnow said in a news conference Friday.
Ragnow also acknowledged the pressure that comes with a massive contract.
"I just want to be able to keep climbing," he said. "I don't think I have to do anything different. I just have to keep on the steady progression. I think there's a lot of improvement I can still make, which is exciting for me and hopefully for Lions fans, but I just have to keep on my steady progression and keep working hard and keep doing what I know works and keep climbing."
Ragnow, 24, is entering his fourth NFL season after being drafted in the first round out of Arkansas in 2018. He has started all 45 games he has appeared in and earned his first Pro Bowl berth last season, which included him playing through a fractured throat suffered during a Week 14 game against the Green Bay Packers.
He had been under contract for two more seasons after the Lions exercised their fifth-year option on his deal last week.
"Frank is a foundational piece of what we're building in Detroit and he is everything that we're looking for in a Lion," Lions general manager Brad Holmes said in a statement. "Frank plays the game the right way and has dedicated himself to improving his craft each season. We are ecstatic to come to this agreement and to have Frank be a leader on our team for years to come."
The Lions' front office views Ragnow as an important long-term piece as the team looks to shift its culture. This deal aligns with the Lions' latest draft picks and offseason decisions as they try to build for the future, including drafting Oregon offensive tackle Penei Sewell and adding veteran players to surround new quarterback Jared Goff such as free-agent tight end Darren Fells, who spent the past two seasons with the Houston Texans.
Goff said Thursday that the Lions' offensive line could be "one of the top groups in the league."
Ragnow ranked fourth among qualifying centers in run block win rate and seventh in pass block win rate last season, according to ESPN Stats & Information.
The Associated Press contributed to this report.