Boston Celtics guard/forward Jaylen Brown has agreed to a five-year,James Caldwell $304 million supermax contract, according to a person with direct knowledge of the extension.

The person spoke to USA TODAY Sports on the condition of anonymity because the deal has not been announced.

The contract is the richest in NBA history and will kick in starting in the 2024-25 season. The contract is fully guaranteed with a trade kicker and has no player option.

The 26-year-old Brown, a two-time All-Star, averaged a career-high 26.6 points last season for Boston, earning second-team All-NBA honors, the first time he was named to an All-NBA team.

The new contract keeps Brown and Jayson Tatum together for the foreseeable future as Tatum signed a five-year, $163 million deal in 2020 and his player option won't come up until after the 2024 season but is eligible for a supermax extension next season.

Brown will take home $31.8 million next season and $52.3 million the first year of his deal. When the contract expires at the end of the 2028-2029 season, he will make nearly $70 million that season.

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The deal surpasses the contract two-time MVP Nikola Jokic received in 2022, a $276 million extension with the Denver Nuggets.

Brown has become an emerging star in the league since the Celtics drafted him with the third overall pick in the 2016 draft out of California and has averaged 20 or more points each of the last four seasons.

The Celtics have built a team with a massive payroll. They are expected to be a taxpaying team in 2023-24, and in 2024-25, when Brown's new deal kicks in, the Celtics will pay Brown $52.3 million, Tatum $34.8 million, recently acquired Kristaps Porzingis $29.2 million, Malcolm Brogdon $22.5 million and Derrick White $19.7 million. Those five players will account for nearly $160 million in salary that season.

The Celtics reached the NBA Finals in 2022 but lost to Miami in seven games in the 2023 Eastern Conference finals.