Five years ago, former Special Air Services Regiment patrol commander Ben Roberts-Smith was considered a national hero.

As Australia's most decorated living soldier, he rubbed shoulders with royalty, was a favourite on the guest speaker circuit and was awarded Father of the Year by a children's charity in 2013.

That came in the same year he left full-time service in the military with such honours as a Victoria Cross, a Medal for Gallantry and a Commendation for Distinguished Service.

Now the 44-year-old's reputation has been lowered so far, a Federal Court judge found, that two unproven allegations of battlefield murder weren't enough to defame him.

Justice Anthony Besanko on Thursday dismissed the veteran's civil action against Nine Newspapers, and found allegations of war crimes, including four unlawful killings, had been established.

Mr Roberts-Smith maintains his innocence and has not been criminally charged but, pending any appeal, has been found to have "disgraced" his country. 

The judge found Nine had established the imputation, through its witnesses, that "the applicant broke the moral and legal rules of military engagement and is therefore a criminal".

He also upheld that Mr Roberts-Smith "disgraced his country Australia and the Australian army by his conduct as a member of the SASR in Afghanistan".

It's a far cry from former prime minister Malcolm Turnbull's comments in April 2018, when he called Mr Roberts-Smith a "great Australian hero".

"He is someone that all Australians look up to, in every respect," Mr Turnbull said, in a nod to the soldier's towering 2-metre frame.

A veteran of six Afghanistan tours, he once acknowledged the praise of political elites "doesn't sit well with me".

After meeting with Queen Elizabeth II as a fresh VC recipient in 2011, Mr Roberts-Smith told reporters: "It is very humbling."

"I think the most important thing to take away is I'm here representing everyone else back home, the whole ADF and more importantly my team who were with me on the day."

The son of a former justice of the Supreme Court of Western Australia and brother of an opera singer, Mr Roberts-Smith grew up in Perth and joined the army at age 18.

After his retirement, he moved to Queensland with his family to study and work.

In 2015, he took over as general manager of Seven's network in that state, a company owned by another famous West Australian — billionaire Kerry Stokes.

Alongside his corporate and public speaking duties, Mr Roberts-Smith was chair of the National Australia Day Council from 2014 to 2017.

Then, in 2018, series of articles from investigative reporters Nick McKenzie and Chris Masters were published in the former-Fairfax newspapers.

They would spark the country's defamation "trial of the century" and change everything for Mr Roberts-Smith.