Over a dozen convicted terrorists could remain behind bars after serving their sentences under a plan approved by states and territories.
Attorneys-general across the country agreed in principle to proposed draft laws which would keep high-risk terrorists locked up beyond their terms after meeting in Canberra on Friday.
Under the measures, a Supreme Court judge must be satisfied there is a high degree of probability a person poses an "unacceptable risk" of committing a serious terrorism offence if released.
They'll stay locked up for a maximum of three years - but there's no limit on how many times their detention can be renewed.
But their continued detention would be reviewed every year.
Federal attorney-general George Brandis said the powers struck the right balance between ensuring community safety and legal protections.
It would apply some states' pre-existing models of post-sentence detention for sex offenders to terrorists.
"This is an unusual power," Senator Brandis told reporters in Canberra.
"This should not be a general feature of our criminal law and it isn't."
The powers would apply to nine terrorists locked up in NSW and four in Victoria.
As well, there are 23 people awaiting trial in NSW on terrorism-related offences, 11 in Victoria and two in Queensland.
NSW attorney-general Gabrielle Upton said the stakes were much higher for her state.
"We have more people in our prison than any other state that would be subject to these laws."
Victorian attorney-general Martin Pakula praised the goodwill between the states and commonwealth, which was echoed by Queensland's Yvette D'ath.
"I do believe it shows a true understanding of the seriousness of the issues that we are dealing with," she said.
The plan needs another sign-off by state and territory premiers and chief ministers.
