The US government has admitted that the terror conviction of Australian citizen David Hicks was invalid, his legal team claims.

Mr Hicks pleaded guilty in 2007 to providing material support for terrorism, but his supporters have argued he only did so under threat of torture.

Lawyer Stephen Kenny says the US government response to a legal appeal from Mr Hicks (which cannot be released) concedes that the conviction cannot be upheld and must be set aside.

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But Mr Hicks may not be able to appeal his original conviction because of a plea bargain he struck, although his lawyer hopes this can be overturned.

“Any court which has made a ruling which is invalid, has the jurisdiction to overturn it. So we fully expect them to do it,” Mr Kenny says.

Mr Hicks is reportedly taking heart from the case of fellow Guantanamo Bay detainee, Noor Muhammed, who had charges against him dropped and his conviction withdrawn this month.

The Australian’s conviction could be overturned “within a month,” says Mr Kenny.

If Mr Hicks does clear his name, he reportedly does not intend to seek compensation from either the Australian or United States governments, simply because there is little chance of succeeding.

“Regretfully, the United States’ courts have always rejected compensation claims because the US government has a policy of stepping in saying `this is a matter of national security’,” Mr Kenny says.

Adelaide-born Mr Hicks was 26 when he was captured in Afghanistan in 2001 by the anti-Taliban Northern Alliance, which believed he was fighting for al-Qaeda.

He was held in the US-run jail in Cuba until 2007, when he pleaded guilty to providing material support for terrorism and was sent to Adelaide’s Yatala Prison to serve the rest of his seven-year sentence.

He was released under a control order later that year.

Former Labor shadow attorney-general Kelvin Thomson said the Howard government had let down Mr Hicks.

“I have always believed that David Hicks’ guilty plea did not make him a guilty man,” Mr Thomson said on his blog.

“He had been detained in Guantanamo Bay in solitary confinement for five and a half years with no recourse to a fair trial.”

Mr Thomson said former foreign minister Alexander Downer did little to secure a fair trial for Mr Hicks.

“It was weak and unworthy – more lapdog than national government,” Mr Thomson said.

In December, Mr Hicks heckled Attorney-General George Brandis at a human rights award ceremony in Sydney.

Labor leader Bill Shorten has told media he is waiting on a response from the US government before commenting.

—with AAP.