Zucker, 41, will succeed Bob Wright, who has headed the network for 21 years, company sources told the Los Angeles Times.
The transition comes as NBC Universal angles itself to compete against online forces such as Google (GOOG), YouTube and MySpace.
Wright, 63, had planned to stay on as CEO at least until the end of the year. But Jeffrey Immelt, chairman of General Electric Co. (GE), the owner of NBC Universal, insisted the change come immediately, according to the company sources, who spoke on condition of anonymity because the switch hadn't been announced.
The casual, creative Zucker is seen as a contrast to the more cerebral and buttoned-down Wright. He has been Wright's second in command since December 2005 and has long been considered the favorite to succeed his boss.
The Harvard graduate joined the network in 1986 as a sports researcher for its Olympics coverage. He moved to "Today" in 1989, and three years later, at 26, became the show's executive producer.
In 2000, Zucker took over NBC's prime-time entertainment division. He kept profits up by extending "Friends" for two additional seasons and by embracing reality shows like "The Apprentice" and "Fear Factor."
Besides its headquarters in New York, NBC Universal has West Coast operations that include Universal Studios, KNBC Channel 4, two Spanish-language television stations, and TV and film production facilities in Universal City and Burbank.