In 2008, Benbrika was found guilty of leading a terror cell that plotted to blow up Australian landmarks.
He was sentenced to 15 years in prison, but remained in custody on a continuing detention order.
He was later placed in immigration detention after former home affairs minister Peter Dutton cancelled his citizenship in 2020.
Benbrika challenged the validity of the part of the citizenship act which allowed his Australian citizenship to be stripped.
In a 6-1 split, the High Court today found the law was invalid, restoring Benbrika’s Australian citizenship.
“The Commonwealth parliament cannot repose in any officer of the Commonwealth executive any function of sentencing persons convicted … of offences against Commonwealth laws,” the judgement read.
“Nor can the Commonwealth parliament vest in any officer of the Commonwealth executive any power to impose additional or further punishment.”
Had Benbrika lost the case, he would have likely faced deportation
PM seeks advice on decision’s consequences
Speaking shortly after the ruling, Prime Minister Anthony Albanese said the government would seek advice on any implications of the decision.
“We will examine the ruling and respond appropriately,” Mr Albanese said.
“Quite clearly there was an issue with the former government’s legislation, which is what this ruling relates to.
“When it comes to the legal consequences, we will seek advice for the ruling and respond appropriately,” he added.
Mr Dutton had said it was “appropriate” for the government to revoke the Australian citizenship of Benbrika, who is originally from Algeria.
“I cancelled the Australian citizenship of convicted terrorist Benbrika, [making him] the first individual to have lost citizenship onshore,” Mr Dutton had said at the time.
In 2005, Benbrika was arrested, along with 16 other men, and charged with various offences.
He was later convicted of intentionally being a member of a terrorist organisation and intentionally directing the activities of a terrorist organisation. ABCnews