Robert Langdon had been sentenced to death for shooting dead a colleague while working to protect a supply convoy under attack from the Taliban in May 2009.
He appealed and has been spared the death penalty, to The Australian newspaper reports.
Documents show that Langdon was secretly sentenced to 20 years in jail in October 2010 after paying ibra, a form of compensation, to appease the dead man`s family, the paper says.
His family in South Australia were unaware of the judgment, the paper says, while AAP`s calls for comment were unsuccessful.
A relative declined to comment when called by AAP.
Calls to his lawyer Stephen Kenny, who is believed to be on holiday, were not returned on Thursday morning.
However Mr Kenny told The Advertiser newspaper he would have to see the decision before deciding what options were available.
"I have not spoken to him (Langdon) yet, but we would be very concerned about a 20-year prison sentence in Afghanistan," Mr Kenny said, according to the newspaper.
Comment was being sought from the Department of Foreign Affairs and Trade (DFAT).
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Editor: Bambang
Copyright © ANTARA 2011
