Lachlan Murdoch has been appointed non-executive co-chairman of News Corp and 21st Century Fox.
The surprise move has sparked intense speculation that the 42-year-old is now strongly favoured to eventually succeed his father, the billionaire media mogul Rupert Murdoch, 83, as head of both companies.
Publishing-focused News Corp and entertainment business 21st Century Fox made separate announcements to stock exchanges in New York and Sydney on Wednesday night (AEDT).
"This appointment is a sign of confidence in the growth potential of News Corp and a recognition of Lachlan's entrepreneurial leadership and passion for news, digital media and sport," said Mr Murdoch senior, News Corp's executive chairman.
"In this elevated role, Lachlan will help us lead News Corp forward as we expand our reach and invest in new technologies and markets around the world."
Rupert Murdoch's younger son James, 41, has been promoted to co-chief operating officer at 21st Century Fox.
Lachlan Murdoch was already listed as a News Corp director, though he effectively walked away from what was then known as News Corporation seven years ago after a reported falling out with senior executives.
Asked by journalists last year if he would consider an executive job at News Corp, Mr Murdoch junior said: "No. No, I've moved on from that."
He will now jointly lead News Corp and 21st Century Fox alongside his father.
Until last year the two companies formed the key pillars of News Corporation, which split in June 2013 following pressure from shareholders, some of whom were worried about the publishing division.
The split also followed allegations of phone hacking at the Murdoch-controlled UK Sunday newspaper, The News of The World.
Lachlan Murdoch's promotion was announced as Australia's Network Ten confirmed he had left his role as the broadcaster's non-executive chairman and director.
He retains his 8.8 per cent stake in the company.
Ten's chief executive Hamish McLennan was appointed executive chairman following Mr Murdoch's departure.
"On behalf of the board I thank Lachlan for the contribution he has made during a very difficult time for the company," said Ten's deputy chairman and lead independent director, Brian Long.
The Ten Network posted a full year loss of $285 million in 2013 and has seen a number of its programs struggle in fierce ratings wars with the rival Seven and Nine networks.
Meanwhile, John Hartigan - the former boss of News Corp's Australian division - was named chairman of Australian tourism organisation Destination NSW on Wednesday.
Mr Hartigan spent 41 years with News Ltd until 2011.
