The U.S. Court of Military Commission Review vacated Hicks' March 2007 guilty plea, the first conviction of a prisoner at the base in Cuba and still one of only a handful.

"We had been waiting for this decision for years," Hicks said at a news conference in Sydney. "It's a relief because it's over."

Hicks, 39, pleaded guilty to providing material support to terrorism. It was a plea bargain in which all but nine months of his seven-year sentence was suspended and he was allowed to return home by the end of that year.

Last year, an appeal's court ruling in the case of another detainee found that material support was not a legally viable war crime for conduct that occurred before 2006, when Congress passed legislation authorizing the special wartime court at Guantanamo known as a military commission. Hicks had been in custody since late 2001.