BSkyB said the deal would create a pay TV provider with 20 million customers across three of Europe's four biggest markets.
Media analyst Claire Enders said the deal shows BSkyB is moving to build business outside its base in Britain and moving beyond direct local competition with BT.
"It's now focused on transporting its technology and its production skills into other markets where there is demand for cutting edge TV," she said. "They believe this phenomenon will come to other countries in Europe, particularly Italy." She said she did not anticipate regulatory obstacles.
James Murdoch, Rupert's son and co-chief operating officer of 21st Century Fox, said the combination of European Sky companies would create "enormous benefits for the combined business and for our shareholders."
Shareholders in BSkyB did not seem excited by the details of the deal, however, pushing the company's share price down 5 percent in London.
BSkyB said it was paying $4.2 billion for Sky Italia and $4.9 billion for its stake in Sky Deutschland. 21st Century Fox would receive cash payments of $8.3 billion and BSkyB would also transfer its 21 percent stake in the National Geographic Channel. The company said it would make a voluntary cash offer to Sky Deutschland's minority shareholders at $9 per share.
Analysts note 21st Century Fox, which has a strong presence in cable, broadcast, film, pay TV and other fields, could use the cash from the European TV deal to help fund its pursuit of Time Warner after the recent failure of an $80 billion offer.
That bid was partly meant to counter consolidation among U.S. TV distributors like Comcast-Time Warner Cable and AT&T-DirecTV.
Time Warner owns TV channels CNN, TNT and TBS, along with the Warner Bros. movie studio, which includes Batman, Superman and Harry Potter. Fox owns the 20th Century Fox movie studio, the Fox broadcast network and such TV channels as Fox News and FX.