The Celtics finalized a flurry of important roster moves Saturday.

Boston signed first-round draft pick Baylor Scheierman to his rookie contract and announced previously reported extensions for starters Jayson Tatum and Derrick White.

Tatum’s five-year, $314 million supermax deal makes him the highest-paid player in NBA history. The 26-year-old has made five straight All-Star teams and three consecutive All-NBA first teams.

“Jayson is a special person and player, and it’s been a thrill for all of us to watch his entire journey in Boston,” Celtics president of basketball operations Brad Stevens said in a statement. “He has embraced all that comes with being a great Celtic, and shows consistent and genuine care for every one of his teammates, coaches, and staff across the organization.

“Despite all the team accomplishments and individual awards, Jayson is committed to constantly improving. He works hard and is extremely driven by the challenges of the game – especially the goal of competing with his teammates for championships. We are obviously ecstatic that Jayson chose to extend his contract and add to his amazing career as a Boston Celtic.”

The centerpiece of the league’s deepest and most talented roster, Tatum led the Celtics in points, rebounds and assists during the 2024 playoffs, becoming just the sixth player ever to do so for an NBA champion. After his extension was announced, the Celtics posted a video of him holding the Larry O’Brien Trophy.

“I’m happy to be here for another five years, for the long haul, and this is what we do it for,” Tatum said. “So I’m looking forward to getting a couple more of these.”

White signed a four-year, $125.9 million extension with Boston rather than waiting for a potentially more lucrative payday in free agency next offseason. The 30-year-old is one of the NBA’s top defensive guards and also was the Celtics’ third-leading scorer during their postseason run (16.7 points per game), trailing only Tatum and Jaylen Brown.

“Derrick is a great player who has immersed himself in the Boston community since joining us in the Spring of 2021,” Stevens said. “Derrick brings a joy and selflessness to our building every single day. He’s committed to improving and has shown that in each year of his career. More importantly, he cares most about the things that matter, including building great relationships and competing with integrity. We are very lucky that Derrick is a Celtic and are thrilled he’ll be here for years to come.”

In addition to locking up Tatum and White, the Celtics also re-signed reserves Luke Kornet, Xavier Tillman and Neemias Queta and picked up Sam Hauser’s team option. Thirteen members of their title-winning roster are under contract for the upcoming season, and all five starters are signed for at least two more years.

The lone new addition to the 15-man roster is Scheierman, a sharpshooting 6-foot-6 wing out of Creighton whom Boston selected 30th overall in the 2024 NBA Draft. Second-round pick Anton Watson, a 6-foot-7 forward from Gonzaga, has yet to officially sign what is expected to be a two-way contract. Both are highly experienced prospects who played five collegiate seasons and will be 24-year-old rookies.

Scheierman, who will wear No. 55 for Boston, is expected to make his Celtics debut at the Las Vegas Summer League, which tips off next weekend. The Celtics’ rookies and young players will face the Miami Heat on July 13, the Los Angeles Lakers on July 15, the Charlotte Hornets on July 17 and the Dallas Mavericks on July 19.

“Man, it feels great. I’m excited to get to work,” Scheierman said in a team-released video after signing his first NBA contract. “I can’t wait to meet the guys. I’m excited for Summer League, obviously, and just get to work and try to get that championship banner No. 19.”

Scheierman averaged 18.5 points and 9.0 rebounds per game last season. He stuffed the stat sheet over his three seasons at South Dakota State and two at Creighton, becoming the first player in men’s Division I history to surpass 2,000 points, 1,000 rebounds, 500 assists and 300 3-pointers in his career.