The NBA's Boston Celtics are being sold to the head of a California private equity firm for US$6.1 billion, a record price for a US sports franchise, according to reports by The Boston Globe.

The newspaper, citing a league source, said the Celtics ownership had agreed to sell the iconic team to William Chisholm, managing director and co-founder of Symphony Technology Group.

It said the US$6.1 billion purchase price is the highest ever offered for a North American sports team, surpassing the US$6.05 billion paid for the NFL's Washington Commanders in 2023.

The sale of the Celtics, the current NBA champions, still requires the approval of the NBA Board of Governors.

The team is one of the most storied in the league's history, with a record 18 championships.

Chisholm, a Massachusetts native, is a longtime fan of the team, according to the Globe.

It said the new ownership group also includes current Celtics co-owner Robert Hale; Bruce Beal Jr., president of Related Companies; and the global investment firm, Sixth Street.

The newspaper said three other buyers had been under consideration: Steve Pagliuca, a Celtics co-owner; Stan Middleman, a co-owner of MLB's Philadelphia Phillies; and The Friedkin Group.

The Grousbeck family and Pagliuca purchased the Celtics for US$360 million in 2002.

Three NBA teams were sold in 2023 – the Phoenix Suns for US$4 billion, the Milwaukee Bucks for US$3.5 billion and the Dallas Mavericks for US$3.5 billion. (AFP)