Former SAS commando Ben Roberts-Smith has been fighting to salvage his tattered reputation since 2018, when papers unearthed allegations he took part in the murder of unarmed Afghan prisoners.

His multi-million dollar bid to sue three Australian outlets for defamation failed in 2023, with a judge ruling the bulk of the journalists' claims were "substantially true".

He tried to appeal the finding, which was dismissed by the Federal Court in May.

Roberts-Smith then tried to get a special leave application to challenge the previous finding, which was rejected Thursday.

A notice on the High Court's website said: "special leave refused with costs" for all related matters.

The lead journalists in the stories, Nick McKenzie and Chris Masters, said in a joint statement that the case had been an "ordeal that all the nation has endured".

"We are grateful to the courts for the sound and thorough deliberations, and to the Australian soldiers who had the moral courage to stand up for what was right and tell the truth about Ben Roberts-Smith," the Sydney Morning Herald, one of the newspapers involved in the case, quoted them as having said.

"They are the heroes of the grim vital story. We also remember the Afghan victims of war crimes whose families are still waiting for justice," they said.