It also found Ben Roberts-Smith "complicit in and responsible for" the murder of four Afghans.
Last week, he lost a defamation suit against three Australian newspapers over war crimes allegations.
It's raised the spectre of a possible wider reckoning over claims of war crimes by Australian forces.
On Thursday, Federal Court Judge Anthony Besanko threw out the former special forces corporal's case against The Age, The Sydney Morning Herald, and The Canberra Times.
Roberts-Smith claimed the papers ruined his life by their reports that he had broken the moral and legal rules of war.
The judge delayed releasing the reasons for his judgement until Monday, to allow Australian authorities time to ensure it did not inadvertently divulge national security secrets.
But Judge Besanko found the claims that Roberts-Smith had murdered unarmed prisoners and civilians while serving in Afghanistan were "substantially true".
Saying that the 44-year-old was "not an honest and reliable witness", he added: "I have difficulty accepting the applicant's evidence on any disputed issue".
He further found that the Victoria Cross recipient invoked a special forces code of silence to intimidate witnesses, and also smeared and threatened others.
In a bid to silence a fellow Afghanistan veteran, Roberts-Smith went to the extent of sending a legal threat to Gina Rinehart, Australia's richest woman, warning that the ex-soldier - Ms Rinehart's relative - would be sued for speaking ill of him.
He even hired a private detective to investigate another former soldier who was questioning his past, producing a report that profiled not only the veteran, but his wife and parents as well.
In a tape recording, Roberts-Smith was also heard lambasting soldiers who break the code of silence. "A few people [in the special forces] had done what we don't do and that's talk out of school."
Roberts-Smith has not commented since the ruling, but he is expected to appeal to the full bench of the federal court.
The 110-day defamation trial cost up to an estimated A$25m ($16.3m, £13.2m).
Roberts-Smith had been considered a national hero for having single-handedly overpowered Taliban machine-gunners who were attacking his Special Air Service (SAS) platoon, earning him Australia's highest military honour.
He was appointed to high-profile executive positions and received a string of accolades, even being crowned Father of the Year in 2013.
But while he has not been charged with any offences, the father of two is currently the subject of an Australia Federal Police inquiry into alleged war crimes committed in Afghanistan.
In 2020, a landmark investigation known as the Brereton Report found "credible evidence" that elite Australian soldiers unlawfully killed 39 people in Afghanistan.
It recommended that 19 current or former soldiers should be investigated over alleged killings of prisoners and civilians from 2009-13.