Australia’s most-decorated living soldier Ben Roberts-Smith, has lost an appeal against a landmark defamation judgement which found he committed war crimes.

A judge in 2023 ruled that news articles alleging the Victoria Cross recipient had murdered four unarmed Afghans were true, but Mr Roberts-Smith had argued the judge made legal errors.

The civil trial was the first time in history any court has assessed claims of war crimes by Australian forces.

A panel of three Federal Court judges on Friday unanimously upheld the original judgement, though Mr Roberts-Smith has said he will appeal the decision to the High Court of Australia “immediately”.

“I continue to maintain my innocence and deny these egregious spiteful allegations,” he said in a statement.

Mr Roberts-Smith, who left the defence force in 2013, has not been charged over any of the claims in a criminal court, where there is a higher burden of proof.

The former special forces corporal sued three Australian newspapers over a series of articles alleging serious misconduct while he was deployed in Afghanistan between 2009 and 2012 as part of a US-led military coalition.

At the time the articles were published in 2018, Mr Roberts-Smith was considered a national hero, having been awarded Australia’s highest military honour for single-handedly overpowering Taliban fighters attacking his Special Air Service (SAS) platoon.

The 46-year-old argued the alleged killings occurred legally during combat or did not happen at all, claiming the papers ruined his life with their reports.

His defamation case – which some have dubbed “the trial of the century” in Australia – lasted over 120 days and is now rumoured to have cost up to A$35m ($22.5m; £16.9m).

In June 2023 Federal Court Justice Antony Besanko threw out the case against The Age, The Sydney Morning Herald, and The Canberra Times, ruling it was “substantially true” that Mr Roberts-Smith had murdered unarmed Afghan prisoners and civilians and bullied fellow soldiers.

He also found that Mr Roberts-Smith lied to cover up his misconduct and threatened witnesses.

Additional allegations that he had punched his lover, threatened a peer, and committed two other murders were not proven to the “balance of probabilities” standard required in civil cases.

The “heart” of the appeal case was that Justice Besanko didn’t given enough weight to Mr Roberts-Smith’s presumption of innocence, his barrister Bret Walker, SC said.

There is a legal principle requiring judges to proceed carefully when dealing with civil cases that involve serious allegations and in making findings which carry grave consequences.

Mr Walker argued that meant the evidence presented by the newspapers fell short of the standard required.

Months after the appeal case had closed, Mr Roberts-Smith’s legal team earlier this year sought to reopen it, alleging misconduct by one of the reporters at the centre of the case.

They argued there was a miscarriage of justice because Nick McKenzie, one of the journalists who wrote the articles at the centre of the case, allegedly unlawfully obtained details about Mr Roberts-Smith’s legal strategy.

The legal team pointed to a leaked phone call between Mr McKenzie and a witness – which The Age, The Sydney Morning Herald, and The Canberra Times said may have been recorded illegally.

But on Friday, the trio of judges rejected that argument too.

They said “the evidence was sufficiently cogent to support the findings that the appellant murdered four Afghan men”.

“To the extent that we have discerned error in the reasons of the primary judge, the errors were inconsequential,” they added.

They also ordered Mr Roberts-Smith to pay the newspapers’ legal costs.

In a statement, Mr McKenzie called the ruling an “emphatic win”.

He thanked the SAS soldiers who “fought for the Australian public to learn the truth”, and paid tribute to the Afghan “victims of [Mr] Roberts-Smith”.

“It should not be left to journalists and brave soldiers to stand up to a war criminal,” he said. “Australian authorities must hold Ben Roberts-Smith accountable before our criminal justice system.”