The former special forces soldier had appealed his 2023 Federal Court loss after he sued Nine Newspapers for defamation over reports claiming he was complicit in the murder of four unarmed civilians in Afghanistan.
Roberts-Smith disputed Justice Anthony Besanko's findings that the allegations were substantially true, arguing that was not backed up by sufficient evidence for such serious claims.
On Thursday, Australia's highest court refused the former soldier's application to appeal the Federal Court findings.
It came on the same day the recipient of Australia's highest two military honours - the Victoria Cross and Medal for Gallantry - was ordered to pay a lump sum of Nine's legal costs for the unsuccessful Federal Court appeal.
The costs of the 110-day trial and the 10-day appeal are estimated to exceed $30 million.
Roberts-Smith's High Court bid had claimed the Full Court of the Federal Court made an error in assuming he had accepted some allegations which were not re-contested during the appeal.
The articles, published in 2018, included claims Mr Roberts-Smith kicked a handcuffed man off a cliff and ordered his execution, and machine-gunned another prisoner, taking his prosthetic leg home as a souvenir drinking vessel.
The alleged war criminal has maintained his innocence, and has not been charged with criminal wrongdoing.
Justice Besanko found Roberts-Smith machine-gunned an unarmed prisoner in the back, taking the man's prosthetic leg back to Australia to use as a beer drinking vessel during a 2009 raid on a compound codenamed Whiskey 108.
Mr Roberts-Smith also stood silent while a rookie soldier was ordered to execute an elderly Afghan prisoner so he could be "blooded".
Justice Besanko found one of the newspapers' central claims - that Mr Roberts-Smith had kicked an unarmed and handcuffed man, Ali Jan, off a 10-metre cliff and then ensured he was shot - was true.
As evidence of his guilt, Mr Roberts-Smith attempted to cover up the unlawful killing at Darwan in September, 2012 by removing Mr Jan's handcuffs and planting a radio alongside his lifeless body before he was photographed.
Mr Roberts-Smith then told fellow SAS soldiers who witnessed the incident to stick to an approved story that Mr Jan was a spotter who they killed legitimately.
The appeal judges firmly rejected the former SAS corporal's claim he did not know allegations of murder at a compound known as Whiskey 108 were true.
When dismissing his appeal in May, the judges noted there were three eyewitnesses to the murder, which they said was a "problem" for Roberts-Smith.
10°C