Ben Roberts-Smith, a former member of Australia's elite Special Air Service regiment, sued three Australian newspapers over stories printed in 2018 that alleged he orchestrated the killings of unarmed Afghan prisoners.

The towering soldier lost the multi-million-dollar courtroom battle in June, with a judge finding the newspapers had proven the bulk of their allegations to be "substantially true".

Roberts-Smith has now reignited the bruising legal saga, with Federal Court documents showing he filed a "notice of appeal" on Tuesday afternoon.

It was not immediately clear on what grounds the appeal was lodged, or when it might be heard in court.

Before the trial, Perth-born Roberts-Smith had been Australia's most famous and distinguished living soldier.

He won the Victoria Cross -- Australia's highest military honour -- for "conspicuous gallantry" in Afghanistan while on the hunt for a senior Taliban commander.

The Age, The Sydney Morning Herald and The Canberra Times shredded this reputation when they published a series of bombshell reports alleging that Roberts-Smith had engaged in a pattern of criminal and immoral behaviour while serving overseas.

The papers reported Roberts-Smith had kicked an unarmed Afghan civilian off a cliff and ordered subordinates to shoot him.

He was also said to have taken part in the machine-gunning of a man with a prosthetic leg, later bringing the leg back to an army bar and using it as a drinking vessel with comrades.

The court ruling ultimately implicated Roberts-Smith in the murder of four unarmed Afghan prisoners.

The case was one of Australia's longest-running defamation trials and local media has estimated the legal costs to be about US$16 million.

Australia has in recent years been forced to reckon with the actions of its troops in Afghanistan, as well as deeper questions surrounding its macho military culture.

A 2020 military investigation found "credible evidence" that special forces personnel "unlawfully killed" 39 Afghan civilians and prisoners, revealing allegations of summary executions, body count competitions and torture by Australian forces.