Laws that allow for Australian citizenship to be stripped from dual nationals suspected of terrorist activities are constitutionally invalid, the High Court has ruled.
In a landmark case, the High Court found on Wednesday the government is unable to strip a person of their Australian citizenship if they are charged with terrorism offences outside Australia.
A majority judgment found that section 36B of the Australian Citizenship Act 2007 "reposes in the Minister for Home Affairs the exclusively judicial function of punishing criminal guilt", a power that should not be held by legislative members.
But the bench also found that it is within the legislative power to enact laws that determine who is an "alien" under the Australian Constitution.
The case was brought by Turkish-Australian man Delil Alexander, 35, who travelled to Turkey in 2013 and then to Syria where he married his wife and where he was accused of being affiliated with terrorist groups, according to the Australian Security Intelligence Organisation (ASIO).
In 2017 Mr Alexander was arrested by Kurdish militia and was sentenced to 15 years' jail by a Syrian court for terrorism-linked offences. The sentence was later reduced to five years.
Mr Alexander's sister Berivan, who launched the action on his behalf, said Syrian officials subjected her brother to torture before receiving his admission.
He was pardoned in June last year, but the then-home affairs minister Karen Andrews cancelled his citizenship despite classified advice from ASIO that did not recommend citizenship cancellation, the court heard.
Since 2021, Mr Alexander's family or legal team have been unable to locate him as he is believed to be in Syrian intelligence custody.
Government lawyers argued the ASIO submission was not required to make any recommendation to the minister on possible action against Mr Alexander.
"The minister's decision ... turns upon both security issues and other issues (such as an assessment of repudiation of allegiance to Australia and the public interest)."
Mr Alexander's solicitor Osman Samin, from Australian Criminal and Family Lawyers, said this was a historic moment in the way in which Australian laws were interpreted.
Mr Alexander has retained his Turkish citizenship and his Australian citizenship will be reinstated.
With AAP.