The former spy, known only as Witness K, appeared in the ACT Magistrates Court for the first time on Thursday, where his plea of "guilty, your Honour" came from a quiet voice behind a wall of black screens shielding him from public view.

The security cameras in the courtroom were taped up, the doors blacked out, and any windows giving a view into the court were covered in black sheeting in the highly unusual arrangements designed to protect the former spy's identity.

It has been three years since he was charged, eight years since the conspiracy offence was committed and Witness K's home raided, and 17 years since the Australian bugging operation.

Witness K was charged with the conspiracy to breach Australian intelligence laws after signing an affidavit that was provided to a tribunal in the International Court of Arbitration. That is all that has been heard in open court of the charge.

At Thursday's sentence hearing, defence barrister Robert Richter QC told the court that the Commonwealth had agreed to not press for immediate jail time. He said the defence would argue for a non-conviction order, and a good-behaviour order.

"Witness K is a much decorated officer," Mr Richter said.

"[He has a] blameless and spotless reputation, which has earned commendations in a very lengthy career."

He said a conviction at this point would have no utility and would only increase the "alienation, anxiety and post traumatic stress disorder" he suffered.

He said since Witness K's home was raided in 2013, the former spy had effectively been confined to his home with the prospect of a conviction hanging over him and with no ability to relieve the suffering by travelling with his wife and enjoying his life, since his passport had been confiscated.

The barrister said the case had been subject to long delays, referencing what he called the "ancientness" of what was said to have been done.

The court opened and closed several times during the afternoon with some of the proceedings held behind closed doors.

Witness K's co-accused, lawyer Bernard Collaery, has pleaded not guilty to similar charges and intends to fight the charge at an ACT Supreme Court trial.

Outside court, much more has been made public about Witness K's role.

In 2004, Witness K, a spy with the Australian Secret Intelligence Service, oversaw a bugging operation ordered by the Australian government on the East Timorese cabinet rooms. At the time, Australia was negotiating with its tiny and impoverished neighbour over lucrative oil and gas reserves and the two nations later signed a treaty over how those reserves were to be shared.

Concerned about what he had seen and the unfair advantage Australia had sought over its close neighbour in the form of millions of dollars, Witness K took his complaint through official channels to the Inspector-General of Intelligence and Security, who later approved Mr Collaery to act as his representative.

In 2013, Mr Collaery arranged for Witness K to give evidence at a hearing overseas about the allegedly illegal bugging operation but his home and office were raided and the brief seized; Witness K was also raided and his passport confiscated. Mr Collaery later spoke to a number of journalists in protest of the raids.

The sentence hearing, before Magistrate Glenn Theakston, is listed for two days.