Endeavor, the entertainment and sports conglomerate, expanded its sports representation business Tuesday by purchasing a stake in BDA Sports Management, the firm led by the influential N.B.A. agent Bill Duffy.

The partnership calls for Duffy, who represents the rising basketball stars Luka Doncic and Sabrina Ionescu, to become an adviser in the sports division of William Morris Endeavor, one of Hollywood’s major talent agencies. Duffy will continue to serve as chairman and chief executive of BDA Sports, which will retain its own branding and represents an estimated 130 players in the N.B.A., W.N.B.A. and professional leagues internationally.

“We don’t really have an uber-N.B.A.-agent in our company,” Mark Shapiro, Endeavor’s president, said in an interview. “I’m certain this will accelerate our growth plan as it relates to representing more N.B.A. players both on and off the court.”

Terms of the agreement were not disclosed, but Shapiro described Endeavor’s stake as a “meaningful, strategic investment.” WME Sports has provided full-service representation for several tennis and golf clients, including the tennis stars Serena Williams and Naomi Osaka, but the sports division’s co-head, Karen Brodkin, said the alliance with Duffy was part of a broader strategy to work with “more clients earlier in their career trajectory” in sports where they haven’t historically. Duffy said the union with WME would position BDA Sports “to build something even bigger and better than what we’ve been able to do.”

“The modern athlete has a high expectation for off-the-court opportunities,” Duffy said. “They want to get into gaming, into fashion, into entrepreneurial endeavors. WME has a history of doing that at the highest level, so with this partnership, it’s like we’re expanding our menu from one page to four.”

Duffy, who turns 61 in January, oversees a team of six agents domestically and seven internationally. He has represented Hall of Fame N.B.A. players like Yao Ming and Steve Nash, now the head coach of the Nets. Duffy’s current clients include Ionescu of the W.N.B.A.’s Liberty and the N.B.A. players Doncic of the Dallas Mavericks, Phoenix’s Deandre Ayton, Chicago’s Zach LaVine, Miami’s Goran Dragic and the Knicks’ RJ Barrett.

A fifth-round draft pick by the Denver Nuggets in 1982 after playing in college at Minnesota and Santa Clara, Duffy began his agent career by representing the former Cleveland Browns wide receiver Webster Slaughter in 1985. Duffy was connected to Slaughter by his boyhood friend Ronnie Lott, the former San Francisco 49ers star and Hall of Famer, and soon moved into basketball representation. He founded BDA Sports in 1996.

Endeavor, which is led by Ari Emanuel and represents entertainers like Denzel Washington and Selena Gomez, has been making other sports moves. The agency’s recent hires include Bret Just, who represents pro and college basketball coaches and N.B.A. front-office executives, and the N.F.L. player agents Brian Ayrault and Ben Renzin, who were lured away from the rival Creative Artists Agency to launch a football group for WME Sports.

The arrangement between WME and BDA Sports is the latest in a string of partnerships between top Hollywood agencies and player-representation companies in both basketball and soccer — the team sports with the most global reach. In July 2019, the prominent N.B.A. agent Rich Paul sold what the buyer United Talent Agency called a “significant stake” in Paul’s Klutch Sports Group to establish Klutch as UTA’s sports division.

Even before their partnership was formalized Tuesday, Duffy’s BDA Sports had enlisted WME Sports’ help with off-the-court pursuits for various clients. Nash’s forays into soccer and basketball broadcasting after he retired as player in 2015 were largely arranged by WME. BDA and WME also each signed Ionescu as a client in the spring, for on- and off-court representation, after the Liberty selected the former Oregon star with the No. 1 overall pick in the 2020 W.N.B.A. draft.

“I’m an ex-athlete and I understand the importance of stability and support during that transition in life when the ball stops bouncing,” Duffy said. “I have to be thinking about longevity for them and their careers always.”

Shapiro said the deal with Duffy’s BDA “would have been done a lot sooner” if not for the coronavirus pandemic. Like other agencies in Hollywood, Endeavor instituted a round of layoffs, furloughs and pay cuts earlier this year. Public events in many of its specialty areas — like Broadway, stand-up comedy, music and fashion — remain “primarily closed,” Shapiro said.