Kevin Reilly is stepping down as chairman of Fox Entertainment on Thursday, according to people familiar with the matter.
The major shake-up comes after the Fox television network wrapped up a bruising season, with ratings for its regularly scheduled shows slumping. Reilly's decision to leave had been in the works for several weeks, and negotiations accelerated this week, according to a person familiar with the matter.
Fox has already begun a search for a successor to Reilly, and was expected to look at outside candidates as well as executives who currently work within the company, according to a second knowledgeable person.
The move occurs at an awkward time. The network just two weeks ago unveiled its new fall schedule for advertisers, which included the DC Comics inspired show, "Gotham," and a comedy starring Will Forte called "Last Man on Earth."
Fox ended the TV season in fourth place in overall viewers with an average of 7.5 million viewers a night, helped in part, by large audiences for NFL football games, including the Super Bowl.
But the network's entertainment slate has struggled for traction.
The network's longtime ratings engine, "American Idol," fell apart this year, losing nearly half of its audience compared to its 2013 run. The aging show, which once drew more than 25 million viewers an episode, mustered 10 million viewers in its finale earlier this month.
Reilly joined Fox in July 2007 as its entertainment president after exiting NBC in a shake-up orchestrated by former NBCUniversal chief Jeff Zucker. Zucker wanted to clear the way to install Ben Silverman as head of the peacock network, a move that badly backfired.
Reilly almost immediately made a splash at Fox, which had been struggling creatively. During Reilly's tenure at Fox, the network launched such hits as "Glee," and "New Girl." Last season, Fox found success with "Sleepy Hollow," and "Brooklyn Nine-Nine."
In August 2012, Reilly was promoted to chairman of entertainment when his boss, Peter Rice, was elevated to oversee all of Fox's entertainment and sports networks.
It was unclear Thursday morning who would replace Reilly, but industry insiders have speculated that John Landgraf, who runs FX networks, or perhaps Dana Walden, co-chairman of 20th Century Fox Television would be in line to take over network programming.
Earlier in his career, Reilly ran programming at FX, helping to establish the cable channel as a destination for edgy entertainment with such shows as "The Shield."
Times staff writer Joe Flint contributed to this report.