The abuse left the now adult victim "riddled with a sense of shame, guilt, remorse, self blame" that led him to abusing alcohol and drugs to "numb the pain and deal with my confusion".

His father, a former Christian minister, pleaded guilty to one count of maintaining a sexual relationship with a young person and two counts of an act of indecency on a young person under 16.

Agreed facts tendered to the court state that the offending happened between 1998 and 2002.

The period involved the offender masturbating the victim or had the victim masturbating him.

During one incident, the victim's mother appeared, giving the victim hope that she would intervene, but the offender gestured for her to leave.

The offender was brought before the ACT Supreme Court on Tuesday when the victim, appearing via video link, read out his impact statement.

"My father, who was supposed to be my protector, my trusted caregiver and my mentor betrayed and deceived me when he chose to gratify his sexual desires through me," he said.

"I later realised the violation and betrayal of my father towards me.

"That realisation only occurred after a long period of hurt and suffering, trying to function as best as I could while suppressing this dark evil in my life."

The victim said his father should have empowered him and imparted wisdom but "you had no interest in building me up".

"I'm now suffering with a brain tumour. Years and years of abuse at your hands have left my mind and body traumatised," he said.

The victim said he self harmed before the attempted suicide.

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Agreed facts state that the victim told a pastor and family members in late 2014 before he confronted his father where he covertly recorded the conversation.

"We used to have - joke and a bit of a belly laugh and just move on," the offender said.

"There was nothing malicious about it. I would feel very offended if someone called me an abuser."

The victim went to police in 2019 after he felt the offender was not taking responsibility for his actions.

During the sentencing hearing, Crown prosecutor Sofia Janackovic said there was "no contest between the parties that a full-time custodial sentence is warranted".

She said the offender's moral culpability was high because he initiated all of the incidents and that during the covert recording, the offender said he knew it was wrong and acknowledged the inequality and illegality, as well as expressing concerns that "the law would catch up to him".

Ms Janackovic said that while the covert audio recording showed that the offender repeatedly apologised to the victim, the court should not have confidence that he had full insight into his offending.

The prosecutor cited his comments in 2014-15 when he described the sexual abuse as a joke and used the phrases "silly me", "my foolishness" and "fun with our penises".

Defence lawyer Jacob Robertson said his client had engaged in treatment starting in mid-2020 to help him develop insight and pathways to meet his emotional needs.

"His insight into his offending is far greater than it was in 2014," Mr Robertson said.

Justice John Burns said it "is very clear to me that a term of imprisonment is inevitable".

He will deliver his sentence on July 28.

The offender, who initially pleaded not guilty before the brief of evidence was served, had his bail revoked following the hearing.

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