Fox Entertainment Chairman Kevin Reilly on Thursday announced his resignation after seven years leading the network, calling his tenure a "satisfying blast."
Reilly said he would step down at the end of June.
"While difficult decisions have to be made every day, none have weighed more heavily on me than this," Reilly told his employees in an email sent Thursday morning. "The inspired Fox leadership, coupled with your commitment to excellence at FBC [Fox Broadcasting Co.], has provided one of the most rewarding chapters in my life."
Reilly's decision comes after a bruising TV season, in which Fox's ratings plummeted.
Its one-time juggernaut, "American Idol," witnessed an exodus of viewers, and Reilly's entertainment division mustered few buzz-worthy hits beyond "Sleepy Hollow," and "Brooklyn Nine-Nine."
Fox already has launched a search for a successor and is expected to look at internal as well as outside candidates, according to people with knowledge of the situation.
Reilly's departure comes at an awkward time. Two weeks ago, he unveiled Fox's new fall schedule, which included the DC Comics-inspired show "Gotham" and a comedy starring Will Forte called "Last Man on Earth."
Advertisers seemed hopeful about the prospects of Fox's new entertainment slate.
Still, Fox faces an uphill slog to remain relevant in an increasingly fragmented media world. The network 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.
"Kevin's undeniable creative gift and passion for talent have left an indelible mark on our company," Peter Rice, chairman and chief executive of the Fox Networks Group, said in a statement.
"We are extremely grateful to him for his leadership, beginning with "The Shield," and "Nip/Tuck" at FX and continuing through "Glee," "The Following," "Sleepy Hollow" and "Brooklyn Nine-Nine" at Fox," Rice said.
During the transition period, senior Fox Entertainment executives and other staff members will report to Rice.