It’s long been thought that the succession plan for Lachlan Murdoch to take control of Fox Corporation and News Corp was set in stone for when his 91-year-old father, Rupert Murdoch dies.

But a new book is stoking speculation that Murdoch’s oldest son might be ousted in a Succession-style feud with his family, in a move with potentially huge ramifications for Fox News, the TV network that dominates US rightwing politics, according to a new biography of the Anglo-Australian media heir.

The author, Paddy Manning, writes: “A Wall Street analyst who has covered the Murdoch business for decades and is completely au fait with the breakdown in the relationship between the brothers [Lachlan and James Murdoch], volunteers off the record that it would be ‘fair to assume Lachlan gets fired the day Rupert dies’.”

The Successor: The High-Stakes Life of Lachlan Murdoch will be published in the US on 15 November and is out in Australia now.

Manning is an Australian journalist who has written for outlets including the Guardian. His previous books include biographies of Malcolm Turnbull, the former Australian prime minister, and Nathan Tinkler, a mining entrepreneur.

The title of Manning’s biography of Lachlan Murdoch echoes that of the TV hit Succession, the HBO story of an ageing media tycoon, played by Brian Cox, and his family’s struggles to succeed him.

Lachlan Murdoch, 51 and Rupert Murdoch’s oldest son, has led the family media businesses with his father since 2014.

James Murdoch, 49, resigned from the board of News Corp in July 2020. He said then: “My resignation is due to disagreements over certain editorial content published by the company’s news outlets and certain other strategic decisions.”

The younger Murdoch has since emerged as a backer of progressive and environmental concerns, in Manning’s words, “ploughing millions into the defeat of [Donald] Trump, climate activism, and other political causes”.

But Lachlan Murdoch has remained in a position of near-unrivaled power in rightwing media and politics, overseeing US properties including the New York Post, the Wall Street Journal and Fox News, the TV network with a near-symbiotic relationship with Trump and the Republican party.

Though Manning reports a potentially surprising $1,500 donation Lachlan Murdoch made in 2020 to Pete Buttigieg, then a Democratic presidential hopeful, now the Biden administration’s transportation secretary, he also reports that “realising the potential for embarrassment, [Murdoch] asked for it back and was duly refunded”.

The Successor covers the older Murdoch son’s life from childhood through youthful business ventures including investment in Australian rugby league, to his departure from his father’s businesses in 2005 and return nearly a decade later.

Lachlan Murdoch has become a champion of the rightward march of Fox News, which inspired his brother’s resignation from the News Corp board. As described by Manning, the older Murdoch son has for example remained supportive of Tucker Carlson, the primetime host and provocateur who regularly espouses far-right views.

But all four grownup Murdoch children – Lachlan and James, their sister Elisabeth Murdoch and their half-sister Prudence MacLeod – will be key players in the eventual succession.

“In a plausible scenario,” Manning writes, “after Rupert has passed and his shares are dispersed among the four adult children, the three on the other side of Lachlan could choose to manifest control over all of the Murdoch businesses, and to do it in a way that enhances democracies around the world rather than undermining them.

“In this scenario, the role of Fox News has become so controversial inside the family that control of the trust is no longer just about profit and loss at the Murdoch properties. In one view that has currency among at least some of the Murdoch children, it is in the long-term interests for democracies around the world for there to be four shareholders in the family trust who are active owners in the business.”

Last month, Rupert Murdoch was reported to be seeking to merge News Corp, which owns newspapers outside the US including the Times, the Sun and the Australian, with Fox, which includes Fox News and Fox Sports, which shows prized NFL games.

A former Murdoch senior executive told the Guardian then the plan had been “in the works for two years. I give it a 75% chance it will happen, 25% that it will be blocked. It’s all about Lachlan. Rupert is in his 90s – this is his last deal, it’s succession planning.”

Discussing the belief that “Lachlan gets fired the day Rupert dies”, Manning writes that it is “a formula for instability and intra-family feuds that must weigh on the minds of directors of both Fox and News Corporation as they contemplate the mortality of the 91-year-old founder, although they deny it.

“A source close to members of the Murdoch family questions the extent of succession planning by the boards of Fox or News Corporation and whether discussions among the directors can be genuinely independent, as corporate governance experts would like.

“‘Rupert has total control over all the companies as long as he is alive,’ the source says. ‘It’s an unrealistic expectation that the boards of those companies are going to use their voices to manifest independence. What is their succession plan? What if something happens to Lachlan?’”