The Commonwealth is prosecuting former military lawyer David McBride in the ACT Supreme Court for allegedly leaking classified documents.
He is facing charges of theft of commonwealth property, breaching the Defence Act and unauthorised disclosure of information.
A subsequent inquiry following his revelations found that Australian special forces committed at least 39 unlawful killings during the Afghanistan war and treated two prisoners with cruelty.
Rex Patrick said the government needed to use the powers it had to stop the trial.
Whistleblower activists are planning to protest the prosecution outside the court before the hearing.
Human Rights Law Centre senior lawyer Kieran Pender said there was no public interest case for prosecuting whistleblowers.
"Today is a dark day for Australian democracy - the truth is on trial," he said.
Former senator and founder of the Whistleblower Justice Fund Rex Patrick said the government needed to use the powers it had to stop the trial.
"We may now see one brave whistleblower behind bars and thousands of prospective whistleblowers lost from the community," he said.
"There was no public interest in this prosecution and that things have come to this is a blight on this government's pre-election commitment to foster and protect whistleblowers."
A spokesman for the attorney-general said the power to discontinue proceedings was "reserved for very unusual and exceptional circumstances".
"As Mr McBride's proceedings remain ongoing, it is inappropriate to comment further on the particulars of their matters," the spokesman said.
The trial is due to begin on Monday and expected to run for three weeks.
