In the piece, which was widely shared on social media, Keane called the former US president "treacherous" and an "unhinged traitor" and suggested that the Murdoch family, which owns and controls Fox News, was an "unindicted co-conspirator".

While the article did not mention Lachlan Murdoch by name, instead referring to the Murdoch family, the Fox CEO and executive chairman claims he was defamed and suffered serious damage to his reputation.

"Murdoch has been gravely injured in his character, his personal reputation and his professional reputation as a business person and company director and has suffered and will continue to suffer substantial hurt, distress and embarrassment," documents he filed with the court say.

The lawsuit targets the publisher behind the Crikey masthead, Private Media, as well as Keane and editor-in-chief Peter Fray.

Murdoch, who has retained high-profile defamation barrister Sue Chrysanthou SC in the lawsuit, is seeking aggravated damages.

He claims Private Media acted with malice and engaged in a "disingenuous promotional campaign" to increase its subscribers by making false claims he had intimidated and threatened the firm over the article.

According to court documents, the article was defamatory by falsely claiming Murdoch entered into an illegal criminal conspiracy with Trump to overturn the US 2020 presidential election and to incite a mob with murderous intent to march on the Capitol.

Crikey has since written numerous other articles on Murdoch, January 6 and the then looming legal action, openly publishing all letters sent between the Fox CEO's lawyer John Churchill and Private Media's solicitors at MinterEllison.

Murdoch said he had not been approached for comment prior to the June 29 article and subsequent related pieces published on the Crikey website, and had only complained to Private Media four times in a five-year period.

He is also seeking injunctions barring the publication and promotions of the allegedly defamatory articles.

In a statement on its website, Crikey said it welcomed Murdoch's lawsuit.

"For almost two months Crikey has faced the threat of legal action by Lachlan Murdoch over an article about Fox News, Donald Trump and the Jan 6 Washington insurrection. Last night, Lachlan Murdoch finally issued his writ. We welcome it," the firm wrote.

Private Media CEO Will Hayward tweeted on Wednesday that Murdoch had "unleashed his legal and financial forces" against the publisher.

"We are determined to fight for our role as journalists to cover important events – in fact, what we published was tame compared to hundreds of articles and commentaries about the role of Fox News and the Murdochs in the US (where, as public figures, they can't sue for defamation)."

Hayward said Crikey could be on the hook for millions of dollars in damages and legal costs as a result of the lawsuit.