SAG-AFTRA, the powerful actors union, said in a statement that it welcomed “any change that results in increased negotiating power for talent as they bargain individual deals with the multibillion-dollar corporations that produce content.”

It added, “We will carefully scrutinize this combination of two storied talent agencies to ensure that performers will benefit from, and are not disadvantaged by, the deal.”

This deal is the industry’s largest since the William Morris Agency merged with Endeavor in 2009, essentially turning Hollywood into a two-agency town. (The mini-major United Talent Agency is the next biggest behind Endeavor and CAA. ICM was behind UTA, having atrophied from its heyday in the 1990s, when it represented Julia Roberts — long since a CAA client.) In the years since, the major agencies have expanded into fresh lines of business involving finance, podcasting, sports and even content production as a way to keep growing, compensate for declining businesses like sitcom syndication and maintain a grip on forms of entertainment that are still taking shape.

Endeavor made its public trading debut in April; it announced a $1.2 billion deal on Monday afternoon to buy the sports-betting company OpenBet from Scientific Games. Even without ICM’s assets, CAA has also built itself into a top sports agency, representing more than 2,000 athletes including Dwyane Wade, Aaron Rodgers, Chris Paul and Cristiano Ronaldo.

CAA and Endeavor recently had a setback in the fast-growing content-production business, however. In negotiating a new agreement with agencies, the Writers Guild of America succeeded in forcing CAA, Endeavor and other agencies to cap their ownership in content-production divisions to 20 percent. In July, CAA sold most of its upstart content studio Wiip to the South Korean-based JTBC Studios.

Mr. Lourd insisted that the forced divestiture played no role in CAA’s decision to buy ICM. He also poured cold water on one of Hollywood’s immediate assumptions about the ICM deal — that CAA was bulking up to prepare for a public offering of its own.

“Does this make that more possible? Sure,” Mr. Lourd said. “But going public — or not — has not driven any of this.”