The Boston Red Sox has gained a global sports celebrity as a partial team owner. LeBron James has purchased a minor stake in the M.L.B. franchise at the exact same time the team’s longtime ownership group received a $750 million infusion from a private-equity firm.

It wasn’t clear how much James spent in the Fenway Sports Group, which owns the Red Sox and Liverpool Football Club, an English Premier League soccer team.

The investment from the private-equity firm, RedBird Capital Partners, puts the value of Fenway Sports Group at around $7.3 billion, including its debt. In addition to the sports teams, F.S.G. owns Fenway Park, Roush Fenway Racing, the NESN regional sports network and Fenway Sports Management, a marketing company.

James, 36, a part of the Los Angeles Lakers who is in his 18th N.B.A. season, has an extensive history with F.S.G.. He originally partnered with Fenway Sports Management at 2011, enabling it to represent his worldwide marketing rights, and as part of that deal took a small ownership stake in Liverpool F.C.. But by investing in F.S.G. itself, James added the Red Sox and other F.S.G. firms to his portfolio.

Maverick Carter, James’s longtime friend and business partner, also spent in F.S.G.. The deal will make the pair the first Black partners in Fenway Sports Group.

The investments, which still requires approval from Major League Baseball, were confirmed by two individuals with knowledge of these, who spoke on condition of anonymity because they were not authorized to talk to the news media before a public announcement from F.S.G.. The Boston Globe first reported the investments from RedBird and James.

James, an Ohio native, has described himself as a lifelong Yankees fan, and he made a stir during the 2007 baseball match when he wore a hat to an American League playoff game in Cleveland. Then he actively rooted for Cleveland at the 2016 World Series, just months after leading the Cavaliers to the city’s first major sports championship in 52 years.

Expanding his role with F.S.G. is one of James’s many ventures off the basketball court, including his Over a Vote group, which aims to fight voter suppression; his work with Carter at SpringHill Entertainment, a production company; and starring in, as well as producing, the movie “Space Jam: A New Legacy,” scheduled to be released this summer.

Though James has the highest profile among the new investors, RedBird’s participation is very likely to have more effect on F.S.G.’s operations.

RedBird Capital Partners is led by Gerry Cardinale, who helped the Yankees and the Dallas Cowboys shaped Legends Hospitality when he previously worked at Goldman Sachs. RedBird recently joined the Yankees, Amazon and many others in buying the YES Network from the Walt Disney Company. RedBird also recently bought an 85 percent stake in Toulouse Football Club, which plays in France’s second football division.

F.S.G. has over 20 investors, who are all called spouses, but it is directed by John Henry, Tom Werner and Michael Gordon. RedBird’s stake in F.S.G. will be around 11 percent, which makes it the third-largest investor, exceeding Gordon’s stake, according to one of those people with knowledge of the offer.

Henry and Werner paid $660 million to the Red Sox in 2002 and roughly $476 million for Liverpool in 2010. Both teams won long-awaited championships under F.S.G. and could most likely be worth multiple billions independently if they had been sold. RedBird’s investment enables F.S.G.’s present partners to cash out some of those gains without relinquishing control of the franchises. According to The Boston Globe, more than $600 million goes to F.S.G. partners.

Whatever money is left can be spent in a range of ways, including upgrading the current teams’ rosters.

After winning their last World Series title in 2018, the Red Sox substantially slashed their payroll, especially trading the star outfielder Mookie Betts to the Los Angeles Dodgers, who later signed Betts to one of the biggest contracts in the game ’s history. Liverpool has won the Champions League and Premier League in recent seasons but has also been reluctant to invest on roster depth, a choice which has caused a crisis this season following a rash of season-ending injuries to major players.