League sources told NFL Media and ESPN that Mahomes' 10-year extension is worth more than $500 million and contains an injury guarantee of $140 million. The team didn't disclose financial details of the agreement.
The contract also includes a no-trade clause, according to NFL Media. Mahomes -- the No. 10 overall pick in the 2017 draft -- had his fifth-year option for the 2021 season picked up in April, putting him under contract with the Chiefs for the next 12 seasons.
It is the largest contract in professional sports history as Mahomes becomes the first athlete with a half-billion-dollar pact. He is the first NFL player to be the highest-paid athlete in professional sports.
MLB star Mike Trout previously held the distinction of being the top-paid athlete in the world when he signed a 12-year, $426.5 million contract with the Los Angeles Angels in March 2019. However, Trout's contract is fully guaranteed.
"This is a significant moment for our franchise and for the Chiefs Kingdom," Chiefs chairman and CEO Clark Hunt said in a statement Monday. "Since he joined the Chiefs just a few years ago, Patrick has developed into one of the most prolific athletes in all of sports.
"With his dynamic play and infectious personality, he is one of the most recognized and beloved figures to put on the Chiefs uniform. He's an extraordinary leader and a credit to the Kansas City community, and I'm delighted that he will be a member of the Chiefs for many years to come."
After the deal was announced, Mahomes posted a video on social media with the caption, "Here to stay."
Chiefs general manager Brett Veach said the agreement was a priority for "quite a while now."
"His abilities are so rare, and to couple that with an incredible personality is outstanding," Veach said of Mahomes. "We're going to continue to do everything we can to surround him with talent, and this deal provides us more flexibility to do that.
"He's obviously an integral part to our success and we're thrilled he's going to be the quarterback of the Kansas City Chiefs for a long time."
Mahomes becomes the fourth quarterback since 2011 to receive an extension before the start of his fourth NFL season. He joins Ryan Tannehill (Miami Dolphins in 2015), Carson Wentz (Philadelphia Eagles in 2019) and Jared Goff (Los Angeles Rams in 2019).
Mahomes, 24, was named Most Valuable Player in the Chiefs' 31-20 win over the San Francisco 49ers in Super Bowl LIV earlier this year, becoming the first signal-caller in league history to win a league MVP and Super Bowl before turning 25. He was the youngest quarterback to be named Super Bowl MVP.
Mahomes has thrown for 9,412 yards with 76 touchdowns and 18 interceptions in 31 regular-season games in his career. In five postseason games, he has recorded 1,474 passing yards with 13 touchdowns and two picks.