The man, known only as Witness K, was handed a three-month suspended sentence in the ACT Magistrates Court on Friday and ordered to be of good behaviour for 12 months.

Friday's sentencing decision follows Witness K's guilty plea to conspiring to reveal classified information about alleged spying in 2004 by Australia on the East Timorese during talks to carve up lucrative oil and gas reserves.

The sentence is the final stage of almost three years of secretive court proceedings brought against Witness K and his former lawyer Bernard Collaery.

Allegedly acting on instructions from then ASIS head David Irvine, Witness K reportedly installed listening devices in the East Timor cabinet room as Australia and the nascent democracy prepared to slice up lucrative resources.

Witness K's identity remains classified, and while judges may believe it to be in the national interest for the facts of the case to be known to the public, the Commonwealth does not.

He has faced years of political and procedural tactics to stop the exposure of tradecraft reportedly used against Australia's friend and neighbour.

The Human Rights Law Centre issued a statement on Friday afternoon expressing its "deep concern" for Witness K, whose whistleblowing revealed that Australian spies had bugged the cabinet office of Timor-Leste "to gain an upper hand in commercial negotiations over natural resources ... that sit beneath the Timor Sea".

The law centre welcomed the fact that Witness K was spared jail time, but said that the fact he was charged and sentenced at all highlighted the need for urgent reform.

"Witness K did the right thing. Whistleblowers should be protected, not punished," senior lawyer for the centre Kieran Pender said.

"This sentencing will have a chilling effect on others who witness wrongdoing. Instead of speaking up and acting in the public interest, they will think twice given the enormous personal risk that comes with doing the right thing. This only serves to make our democracy poorer."

Australian Associated Press