Former Guantanamo Bay detainee David Hicks will launch an appeal against his conviction for supporting terrorism next month, his lawyer says.
The move comes amid renewed pressure to shut the controversial military jail, with President Barack Obama and former Guantanamo Bay chief prosecutor Colonel Morris Davis - the man who charged Hicks - calling for its closure.
Hicks' Australian lawyer Stephen Kenny said documents were being prepared for the appeal, which he anticipated would be launched in the US next month.
"We expect it to take up to one year to reach resolution," Mr Kenny told AAP.
Hicks spent more than five years in Guantanamo Bay before being transferred to Adelaide's Yatala Labour Prison in 2007 and was released in December that year.
The 37-year-old South Australian admitted providing material support to terrorists as part of a plea deal which facilitated his transfer to Australia.
His bid to overturn the conviction comes after a US court last year quashed a similar charge of material support for terrorism relating to Salim Hamdan, Osama bin Laden's former driver.
Hamdan had his conviction thrown out after the US appeals court ruled in October 2012 that the charge was unlawfully applied retrospectively.
Mr Kenny says Hicks remains in Australia and continues to struggle with the impact of his detention.
"I think he still struggles with the impact of solitary confinement but he's doing the best he can," he added.
President Barack Obama on Wednesday renewed his bid to close Guantanamo Bay, telling a White House press conference it was damaging US interests, amid a widening hunger strike among inmates.
Colonel Morris Davis (retired), chief prosecutor for the Guantanamo Bay military commissions between 2005-2007, added to the pressure with an online petition on Change.org calling for the jail to be closed.
Col Davis, who charged Hicks, Hamdan and Canadian teenager Omar Khadr with terror-related offences, said closing Guantanamo Bay was "the patriotic thing, the American thing, the human thing to do".
The petition had gained almost 40,000 signatures of support by Wednesday morning.
Mr Kenny welcomed the petition.
"Col Davis is an intelligent man and obviously a good lawyer," Mr Kenny told AAP.
"He realised the military commissions were skewed - they did not provide a proper and fair trial for the accused.
"He's realised that Guantanamo is an abomination, an affront to all people who stand up for the rule of law."