Former Northern Territory police commissioner John McRoberts has been sentenced to three years in jail, to be suspended after 12 months, for attempting to pervert the course of justice.

Key points: The former NT police commissioner will spend a year in jail

The former NT police commissioner will spend a year in jail In 2014, he failed to disclose he was in a sexual relationship with the key target of a fraud investigation

In 2014, he failed to disclose he was in a sexual relationship with the key target of a fraud investigation The Acting Justice said John McRoberts had effectively lied by omission

Last month a jury took nine hours to find McRoberts guilty of the offence, which carries a maximum prison term of 15 years.

The jury found McRoberts tried to "frustrate" or "deflect" a travel agent fraud investigation known as Operation Subutai between May and November 2014.

McRoberts had been in a sexual relationship with the investigation's priority target, former travel agent and NT Crime Stoppers chairwoman Xana Kamitsis, who was sentenced to almost four years' imprisonment on fraud and corruption charges in 2015.

Acting Justice Dean Mildren took less than an hour to summarise the evidence and deliver his sentence at Darwin's Supreme Court on Tuesday morning.

"As commissioner, the public has the right to expect that you can be trusted absolutely," he said.

"There is a huge fall from grace."

Between May and November 2014, McRoberts failed to disclose he was in a sexual relationship with Kamitsis.

At the time, McRoberts knew Kamitsis had become a test case for the investigation, which was looking into 27 travel agents suspected of defrauding the NT Health Department's pensioner travel concession scheme.

Acting Justice Mildren said McRoberts had effectively lied by omission.

"You failed to disclose to your staff that Kamitsis was an intimate friend and indeed a sexual partner," he said.

"The relationship between you was a secret one.

"From the moment that you became aware that Kamitsis was a suspect in Operation Subutai, you knew that full disclosure was required in some form and you also knew you should have no further involvement."

McRoberts' lawyer has filed an appeal of his conviction and an application for bail in relation to the matter is expected to be heard by a Supreme Court judge on Wednesday morning.

McRoberts 'hopelessly conflicted': prosecution

During the trial, the prosecution argued McRoberts involved himself in the investigation, knowing he was "hopelessly conflicted", because he wanted stop his relationship with Kamitsis being exposed through a search warrant.

It was alleged McRoberts' criminal course of conduct began in May 2014, when he raised the idea of an alternative civil approach to Operation Subutai, which was then further developed.

McRoberts was also accused of frustrating the execution of a search warrant against Kamitsis in June 2014, by saying to his senior officers: "This is not ready to go to an overt investigation".

During the sentencing hearing, prosecutor Mary Chalmers told the court McRoberts abused his position of power and his sentence should reflect this.

"[The crime] is one that strikes at the very core of the integrity of the administration of justice," she said.

"He abused his position to achieve his ends."

Defence lawyer Anthony Elliot argued his client's conduct was less serious than other cases of attempting to pervert the course of justice.

"We accept that he made a bad decision … that he will continue to pay for, for the rest of his life," he said.

"We accept that he should not have had anything to do with the Kamitsis inquiry.

"But we submit that he was placed in the difficult position of it being intertwined with all the others."

Ms Chalmers told the judge McRoberts engaged in "sustained criminal conduct", which amounted to much more than a single "bad decision".

Alexandra 'Xana' Kamitsis (C) was engaged in an affair with McRoberts in 2014. ( ABC: Xavier La Canna )

No recognition of wrongdoing, remorse: judge

During the trial, more than 5,000 text messages between McRoberts and Kamitsis were submitted as evidence of their relationship.

In his sentencing, Acting Justice Mildren said McRoberts deliberately set out to lead police investigators away from his lover.

"Your purpose from at least sometime in about May 2014 was to frustrate and deflect an imminent prosecution of Kamitsis, your motive was to protect Kamitsis as well as yourself from the scandal that access to her mobile phone would inevitably give rise to," he said.

He said the offence struck at the heart of the administration of justice.

"It involved a gross misuse of power for primarily personal reasons," he said.

"You were, as commissioner of police, expected to uphold the law, not actively to seek to breach it."

Acting Justice Mildren accepted that McRoberts was unlikely to reoffend, and said there was no need to consider special deterrence.

Regarding character references that spoke highly of McRoberts as a police officer and as a person, he said: "You did your best to make a worthwhile contribution to the community that you served", however, he found that McRoberts lacked remorse.

"You have not shown at any stage any recognition of your wrongdoing or any remorse from your actions," Acting Justice Mildren said.

He said the offending was too serious to allow McRoberts to serve his sentence in home detention, and acknowledged his time in prison would be difficult as he has no family in the NT.

"I accept that it will be harder for you … as you will need to be isolated from other prisoners to some degree," he said.