Justice John Burns on Wednesday sentenced the 69-year-old man, who cannot be named in order to protect the victim's identity, to three years and two months in jail.

He ordered the man to serve a non-parole period of 20 months for his "warped" crimes.

Agreed facts tendered to the ACT Supreme Court show the offender carried out the disgraceful abuse between 1998 and 2002, when his son was aged between 11 and 15.

The victim was able to recall the details of two specific incidents, the first of which happened when he was still at primary school.

He was watching cartoons with his father in the loungeroom one afternoon when they began to play fight.

The offender used this as an opportunity to touch the boy's genitals, then perform a sex act on him.

The pastor's wife appeared in the doorway at some stage, but he waved her away with one hand while masturbating his confused son with the other.

On another occasion, shortly after the victim had started high school, the pastor kissed him in a bedroom and forced the boy's hand onto his penis.

There was "regular sexual activity", too, with the victim describing how his father would "summons" him to his parents' bed on Saturday mornings.

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Many years passed before the victim confronted his father in 2014 and covertly recorded their conversation.

The pastor admitted what he had done but attempted to minimise his conduct, saying they "used to have ... a bit of a belly laugh" about it and "just move on".

He added that he would be "very offended if someone called me an abuser", passing his crimes off as "foolishness".

"Silly me," he said at one stage in the taped exchange. "Sinful me."

The pastor later stood down from his role with the Christian Reformed Church, and the victim took the recording to police.

The offender ultimately pleaded guilty in April to one charge of maintaining a sexual relationship with a child, and two counts of committing an act of indecency on a child.

In sentencing on Wednesday afternoon, Justice Burns said the 69-year-old had abused his role as a father and exercised control over a boy who had loved and trusted him.

The court heard last week from the victim, who said he had attempted suicide and now lived with a brain tumour as a result of the pastor's "dark evil".

Justice Burns said the now adult victim's impact statement made it clear the abuse, which occurred in a place he should have felt safe and nurtured, had "blighted" his life.

"There is clear evidence that your offending has had a devastating impact on your son," the judge told the pastor.

"You presented yourself to the world as a man of God, promoting Christian values, while in your home you engaged in conduct that was the very antithesis of what you preached."

Justice Burns said it was not his job to sentence the 69-year-old for hypocrisy, but the man's actions had "warped" his son's understanding of what was right and wrong.

The judge ultimately imposed the jail sentence, which was backdated by eight days to account for the offender's bail having been revoked last Tuesday.

The 69-year-old man, who wore a blue face mask as he appeared in court via audio-visual link from the Alexander Maconochie Centre, did not visibly react.

He will become eligible for parole in March 2023.

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