The reigning NBA champion Boston Celtics have agreed to a $US6.1 billion ($A9.7 billion) sale to a group headed by private equity firm Symphony Technology Group co-founder William Chisholm.

The sale, still pending approval from the NBA Board of Governors, would break the record for most expensive sports team purchase in North America, eclipsing the $US6.05 billion ($A9.63 billion) paid for the NFL's Washington Commanders in 2023.

"Bill is a terrific person and a true Celtics fan, born and raised here in the Boston area," Celtics majority owner Wyc Grousbeck said in a news release on Thursday.

"His love for the team and the city of Boston, along with his chemistry with the rest of the Celtics leadership, make him a natural choice to be the next Governor and controlling owner of the team."

Grousbeck will continue in his roles of Celtics CEO and Governor, overseeing team operations, through the 2027-2028 NBA season.

"Growing up on the North Shore and attending college in New England, I have been a die-hard Celtics fan my entire life," Chisholm said.

"I understand how important the Celtics are to the city of Boston – the role the team plays in the community is different than any other city in the country.

"I also understand that there is a responsibility as a leader of the organization to the people of Boston, and I am up for this challenge."

The Celtics, who lifted their 18th NBA championship last year to break a tie with the Los Angeles Lakers for the most in league history, announced last July their intention to sell the team.