Former SAS corporal Ben Roberts-Smith, who won Australia's highest military honour the Victoria Cross for his actions in Afghanistan, had sued three Nine Entertainment newspapers and their journalists over articles that accused him of killing unarmed Afghan civilians outside the rules of war.
He called the reports false and based on claims of failed soldiers who were jealous of his accolades, and sought unspecified damages.
But a Federal Court judge ruled in June that the newspapers had proven most of their allegations.
The civil court defamation finding required a lower threshold of proof than a criminal court would. Roberts-Smith, 45, whose portrait hangs in the Australian War Memorial, has not been charged with any crimes.
He filed an appeal in July, which is being contested by the three Nine-owned newspapers. The 10-day hearing is scheduled to run until Feb 16.
The appeal will argue the first judge "erred" in his findings and will raise issues including the reliability of several witnesses.
Roberts-Smith declined to comment via his lawyers.
Roberts-Smith has previously called the civil court judgment against him as a "terrible outcome" and said he remains proud of his actions in Afghanistan.
Nine Entertainment has previously said the court's initial judgment is "comprehensive and categorical".
The lengthy legal battle has racked up huge costs for Roberts-Smith and his financial backer, Seven West Media chairman Kerry Stokes.
The Sydney Morning Herald reported Stokes in December agreed to pay legal costs for two of the newspapers involved, estimated at A$16 million ($10 million).
One of the orders sought in the appeal is for all costs in the initial trial and appeal to be paid by the newspapers being sued, according to court documents.
