A former senior spy known as "Witness K" has pleaded guilty in the ACT Magistrates Court to conspiring to reveal classified information.
Witness K had been charged with conspiring with his then-lawyer Bernard Collaery to reveal information about alleged spying by Australia on the East Timor cabinet during sensitive oil and gas treaty negotiations.
In 2019 Witness K indicated he would plead guilty to the charge, but his case has been slow to move through the courts, and it was not until Thursday that he formally entered his plea before a magistrate.
The former spy is facing a sentencing hearing that, barring any further disputes over the facts of the case, will run for two days and determine what punishment he will face.
The ACT Magistrates Court mandates that an accused must plead in person, so during Thursday's plea, Witness K was concealed behind tall black screens in a corner of the court, to keep his identity secret.
Witness K and Bernard Collaery charged under Intelligence Services Act
Both Witness K and Mr Collaery were charged in 2018 with conspiring to reveal secret information.
The charge related to allegations Australian government agents bugged the cabinet room of East Timor during sensitive negotiations between the countries on oil and gas.
Witness K and Mr Collaery were each charged with a single count of conspiring to share information protected by section 39 of the Intelligence Services Act, which covers secrecy and the unauthorised communication of information.
Mr Collaery has chosen to fight his charge at trial.
