Rupert Murdoch is retiring from the Fox and News Corporation boards, the companies announced Thursday morning, making his son Lachlan the sole executive in charge of the powerful global media empire he built from a small local newspaper concern in Australia starting 70 years ago.

The elder Mr. Murdoch will become chairman emeritus of the two businesses, the companies said.

Mr. Murdoch, 92, had shown no intention of stepping down or even slowing down — including after he named Lachlan as the operating heir to his business empire in 2019, when he sold his vast entertainment holdings to the Walt Disney Company.

Even now, in his emeritus status, he will continue to offer counsel, Lachlan Murdoch, 52, said in a company release. And the elder Mr. Murdoch indicated in a statement to employees that he intended to be active in providing that counsel.

“We have every reason to be optimistic about the coming years — I certainly am, and plan to be here to participate in them,” he wrote. “When I visit your countries and companies, you can expect to see me in the office late on a Friday afternoon.”

But the announcement was nonetheless potentially epochal, marking at least the formal end to an active career during which Mr. Murdoch built the most important and politically influential media empire on the planet. His companies, infused with a brand of right-wing populism, have amassed the power to shape, and at times make or break, presidents and prime ministers.

He built that empire across three continents, helping to shift norms and tastes in journalism, politics and popular culture throughout the English speaking world. Using a self-professed pirate’s sensibility, he acted with a willingness to move fast and break things — before that became trendy.

Those tactics also drew legal trouble and a steady stream of condemnation from critics and even onetime allies, especially after stars of his Fox News Channel embraced former President Donald J. Trump’s 2020 election lies — leading to a $787.5 million settlement with the company at the center of so much of it, Dominion Voting.

Lachlan Murdoch, though striking a different visage than his father — with tattoos and trademark leather boots — has so far represented continuity for the family companies. Though he has taken a more aggressive stance in entering the streaming sphere — acquiring the ad-supported entertainment streaming service Tubi in 2020 which has since gained in value — he has maintained the positioning of the companies’ more stridently conservative outlets.

He was in his current role overseeing Fox News in 2020 and had been initially supportive of the network’s far-right firebrand Tucker Carlson. Though he was also credited inside the company with forcing Mr. Carlson from the Fox lineup after the Dominion settlement in the spring, there is no indication the younger Mr. Murdoch will change the network’s overall course and hard-right approach in the lead-up to another presidential campaign that may well have Mr. Trump atop the Republican ticket.

Until now, Lachlan Murdoch has not stepped forward in any aggressive fashion to be the defining face of the company the way his father had been, and the political and media worlds will be watching closely to see if he takes the retirement as an opportunity to do so.

There was no precipitating event for the elder Mr. Murdoch’s announcement, beyond the obvious fact that even the healthiest 92-year-old is in his twilight years.

And it has long been said among those who know Mr. Murdoch that he would prefer to retire while still viewed as sharp and active — he was on the Fox lot this week — than as a diminished figure.

But with his announced retirement, Mr. Murdoch was also further solidifying the company beneath his chosen business heir ahead of a looming, family battle for control of the empire after Mr. Murdoch’s eventual death.

Under the terms of the trust that controls the family’s stake in the empire, each of Mr. Murdoch’s four eldest children — Lachlan Murdoch, Elisabeth Murdoch, James Murdoch and Prudence Murdoch — will have an equal vote on its future following his death; until then, Mr. Murdoch holds the controlling vote.

Rupert Murdoch’s retirement in a sense formalizes the arrangement he had already put in place after the Disney sale, which made Lachlan the day-to-day executive in charge of the two companies at the heart of the Murdoch empire — Fox Corporation and News Corporation.

To wit, the younger Murdoch’s titles — executive chairman and chief executive — remain effectively unchanged, barring the small tweak of losing the “co-” he once shared with his father, who maintained similar titles until Thursday morning.

Mr. Murdoch’s move to anoint Lachlan as his chosen successor was followed by a rift with his younger son James, who is more left-leaning than his father and brother and had been an advocate, for instance, of a less strident and rock-ribbed version of Fox News.

He and his wife, Kathryn, have criticized climate change denialism at the family outlets, and James appeared to be referencing Fox News when he linked the Jan. 6, 2021, attack on the U.S. Capitol to “outlets that propagate lies to their audience, in an interview with The Financial Times.

People close to James Murdoch have raised the possibility that he would seek to rally his two sisters to vote with him to wrest control of the company away from Lachlan after their father’s death and reorient the company away from its defining populism.

But it is unclear whether he would have the votes or ultimately truly want to force that sort of bruising family fight. And if Mr. Murdoch has his way, such a decision would be a long way off. He has often noted that his mother, Dame Elisabeth Murdoch, died just shy of her 104th birthday. As he wrote to employees Thursday, “Our companies are in robust health, as am I.”

This is a developing story. Check back for updates.