Ben Roberts-Smith, a former member of Australia's elite Special Air Services regiment, sued three newspapers after 2018 reports alleged he was involved in the murder of six unarmed prisoners in Afghanistan.

Roberts-Smith denied the allegations and launched a multi-million-dollar defamation case in response.

But Justice Anthony Beskano said the papers had proven many of their allegations were "substantially true" and dismissed the case.

The verdict was hailed as a major victory for Australian media freedom, with journalist and defendant Nick McKenzie tweeting: "Justice."

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

He won the Victoria Cross -- Australia's highest military honour -- for "conspicuous gallantry" in Afghanistan, where his unit was hunting for a senior Taliban commander.

But The Age, The Sydney Morning Herald and The Canberra Times alleged that behind Roberts-Smith's lauded public persona lay a pattern of criminal behaviour.

The paper said 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 Australia and using it as a drinking vessel with other soldiers.

The towering veteran was also accused of domestic violence against a woman in a Canberra hotel -- something the ruling said had not been completely proven -- and of engaging "in a campaign of bullying" against a fellow soldier.

Roberts-Smith and his lawyers had claimed that five of the killings took place in combat, while the sixth was entirely fictitious.

The newspapers and their journalists had backed their reporting throughout the trial, primarily relying on the defence of truth.

The case became one of Australia's longest-running defamation trials, with 40 witnesses providing often harrowing evidence about the behaviour of Australia's special forces.

Local media has estimated the legal costs have run to US$16 million, making it one of the costliest defamation cases in the country's history.

Lawyers for the media indicated they would be seeking "indemnity costs against the applicant" at a later date.

Roberts-Smith's defence was partially bankrolled by the boss of Seven West Media, a rival to the three newspapers.

He was photographed holidaying in Bali ahead of the ruling and did not attend court.