Jaylen Brown averaged career highs of 26.6 points, 6.9 rebounds and 3.5 assists last season. Michael Dwyer/Associated Press

Determined to solidify an All-Star pairing that has delivered four trips to the Eastern Conference finals in the past six seasons, the Boston Celtics on Tuesday agreed to sign guard Jaylen Brown to a five-year supermax contract extension worth $304 million, a person with knowledge of the situation confirmed.

The extension, which will begin in the 2024-25 season, is the richest deal in NBA history. It will keep the pair of Brown and franchise forward Jayson Tatum together for at least the next two seasons.

Brown, 26, became eligible for the lucrative supermax extension when he earned All-NBA second-team honors this past season. He averaged career highs of 26.6 points, 6.9 rebounds and 3.5 assists per game in his seventh professional season, but he faltered at times during the playoffs and Boston lost to the Miami Heat in the Eastern Conference finals.

The Celtics, who were two wins away from winning the NBA title in 2022, entered this summer facing some hard questions after a perplexing showing against the Heat: They fell into a 3-0 series hole before pulling even and were ultimately eliminated with a Game 7 loss on their home court at TD Garden. Boston’s offseason options included splitting up the Tatum and Brown pairing or retooling its supporting cast around the two All-Stars.

Brown’s uncertain contract status loomed large, because the Celtics needed to decide whether it was worth doubling down on a duo that has delivered consistent playoff success but hasn’t been able to get over the hump and win a championship. Last summer, Brown’s name surfaced in trade rumors surrounding then-Brooklyn Nets star Kevin Durant, creating some doubt about his long-term future in Boston.

“He’s one of the best players in this league,” Tatum said after losing in the East finals in May. “He plays both ends of the ball and still is relatively young. And he’s accomplished a lot so far in his career. So, I think it’s extremely important.”

Tatum and Brown are both big, two-way wings – a coveted and rare archetype in the modern NBA – and Boston General Manager Brad Stevens’s early moves this summer suggested he still believed in the tandem. Rather than seriously shop Brown in trades, Stevens traded guard Marcus Smart in a three-team deal that netted big man Kristaps Porzingis in an effort to positionally rebalance his roster. Brown is bigger, younger and more explosive than the 29-year-old Smart, whose play slipped slightly last season.

Adding Porzingis gives the Celtics another scoring option when Tatum and Brown don’t have it going in the playoffs, and moving on from Smart helped clear a backcourt log jam and create a larger role for Derrick White. With White and Porzingis in place around Tatum and Brown, the Celtics should continue to rank among the league leaders in 3-point attempts, a key goal for Coach Joe Mazzulla.

If the Celtics had been interested in trading Brown rather than retaining him, they probably would have placed greater value on keeping Smart’s skills as a perimeter defender. Boston also lost backup forward Grant Williams to the Dallas Mavericks in free agency, a development that should make it easier to field a competitive roster around Tatum and Brown, who will combine to make more than $84 million in the 2024-25 season.

Despite the losses of Smart and Williams, Boston still has several quality defensive pieces, including White, Brown, Tatum and centers Al Horford and Robert Williams III.

For Brown, the No. 3 pick in the 2016 draft, this supermax contract helps compensate for what was viewed as a team-friendly four-year, $106 million rookie contract extension he signed in 2019. Brown enjoyed a breakout season immediately after inking that deal, and he generally outperformed his contract over the past four seasons.

Living up to a $300 million contract will be a trickier proposition, though the NBA’s strong economic outlook and rising salary cap should make deals of this size more common in the coming years. The NBA and the National Basketball Players Association finalized a new collective bargaining agreement in June, and the league is headed for new negotiations with its television partners that could double the league’s media rights revenue.

Brown, a two-time All-Star, must improve as a facilitator and a ballhandler if Boston is going to capitalize on its strong run in recent years and win a championship. In the 2023 playoffs, he averaged 3.4 assists per game against 3.3 turnovers per game, and he committed eight turnovers in Boston’s Game 7 loss to Miami.

That performance was not an anomaly; Brown committed 10 combined turnovers in Games 5 and 6 of the 2022 NBA Finals against the Golden State Warriors. His ball control issues were a key limiting factor when Boston squandered a 2-1 series lead to lose in six games to Golden State.