Dawn Airey, who oversees satellite channels including Sky One, Sky Movies and Artsworld, is to leave BSkyB in the spring to join a major new media firm.
Dawn Airey will leave BSkyB in the spring to take up her new role
Ms Airey has spent almost four years in charge of non-sports output at BSkyB as managing director of channels.
Previously Five's chief executive, she was linked to the vacancy as head of ITV until Michael Grade's appointment.
She will become chief executive of Iostar, which has plans to work across TV, cinema, music and advertising.
BSkyB chief executive James Murdoch said: "Dawn has made a significant contribution to Sky's appeal to millions of customers.
"She has been a valued colleague and a trusted friend. When the time comes, we will wish her well for the future."
Lost was one of the big signings to Sky One during Ms Airey's reign
According to Companies House, the Iostar group was set up in November.
The 12 companies listed include Iostar International Television Distribution, Iostar Television, Iostar Advertiser Media, Iostar Music Publishing and Iostar Films.
While precise details of the group's activities have not been revealed, it appears to be offering a "one-stop shop", covering numerous media.
Susan Thompson, deputy news editor of trade magazine Broadcast, said: "There'll be a reshuffle of the executives [at BSkyB], I'm sure, early next year. But it certainly can cope without her."
Ms Airey made "a very good move" in appointing Richard Woolfe - former director of programmes at Living TV - as controller of Sky One, Ms Thompson added.
"He's only been in the job a few months, but so far so good. He brought Lost to the channel and livened it up a little."
But Ms Airey "doesn't really have control of sports, and a lot of the movie deals are long-running so not a huge part of her remit either", Ms Thompson said.
Hogfather, with David Jason, is one of Sky One's Christmas highlights
The Iostar approach was "starting from scratch, bringing a lot of companies under one banner", she said.
It was innovative but would not necessarily mark a major change in the way the industry worked, she added.
Ms Airey's departure from BSkyB will see additional responsibilities handed to Sky Sports managing director Vic Wakeling and Mike Darcey, the company's chief operating officer.
Mr Wakeling will now take charge of Sky News on top of his existing role, while Mr Darcey is to oversee advertising sales and other activities including its broadband presence.
The company, which has 8.25 million subscribers, will now seek a new head of entertainment and film channels.