(Lawyer) Dennis Edney told CTV News on Saturday that if the 26-year-old is successful, he will walk free.

"We're arguing now that charges upon which he was convicted are not recognized internationally as law of war charges," he said.

Toronto-born Khadr is currently being held in Ontario's maximum security Millhaven Institution. He was transfered to Canada last September from Guantanamo Bay, where he had been held for a decade.

Khadr had pleaded guilty before a military commission in October 2010 to five war crimes -- among them killing a U.S. special forces soldier -- committed as a 15-year-old in Afghanistan. He was given a further eight years behind bars.

Edney said he is confident in the appeal, as the American appeal court has already thrown out similar military commission verdicts made against two other former Guantanamo Bay detainees after ruling the crimes did not exist under international law at the time.

However, Edney said Khadr's case could be more difficult since he had pleaded guilty.

Edney said he plans to file the appeal "in a matter of weeks" and anticipates it will be heard in about a year.

He said Khadr will remain in custody until the appeal is heard.

Under Canadian law, Khadr will be eligible for a parole hearing in July, at which point he will have served one-third of his sentence.