A County Court judge in Melbourne regarded the facts of the case as "disturbing and repugnant".

Judge Sue Pullen on Tuesday told Timothy Christopher Lyth his crimes were aggravated by his gross breach of trust to the victim and her parents, the lengthy period of offending, her age and the disparity in age between them.

Judge Pullen said a psychiatrist reported that Lyth, 31, an unemployed IT worker, had displayed a "callous" attitude when speaking about the acts he committed and that to police he had tried to deflect blame and/or "suggest initiation" of his conduct onto the victim.

Lyth, of Ballarat, had earlier pleaded guilty to a charge of persistent sexual abuse of a child under the age of 16 between 2010 and February this year.

The court heard his offending was revealed when MD - which was how the victim was identified in Judge Pullen's sentencing remarks - told her mother about a sex act with Lyth.

The woman later recorded on her mobile phone further disclosures by MD and confronted Lyth after he returned from church.

In her sentencing remarks, Judge Pullen said courts had a duty to protect children as they are "vulnerable and especially vulnerable to abuse of trust".

"They are immature in their understanding of right or wrong and are dependant upon adults responsible for their care not to abuse that immaturity," she said.

In fixing a maximum of eight years jail with a non-parole period of six years, Judge Pullen also took into account Lyth's lack of previous offending, his admissions to police, and his guilty plea which saved the time and cost of a trial and meant witnesses did not have to give evidence.

Prosecutor Luisa Di Pietrantonio had not found a previous case with a victim as young as MD or one that involved offences over virtually the whole of a person's life.

Ms Di Pietrantonio had submitted it was clear sexual gratification was the reason for Lyth's offending.

Lyth's lawyer Chen Yang conceded that the offending was very serious and that the 25-year maximum prison term for the offence reflected how parliament regarded such conduct.

Judge Pullen was prepared to accept that Lyth's guilty plea indicated some remorse, but noted with "some concern" a psychiatrist's observation that he "overall had a very callous attitude when speaking" about the sex acts.

She said that if he had not pleaded guilty, and been convicted after a contested trial, she would have jailed him for 12 years with a minimum of 10 years.

Lyth will be placed on the sexual offences register for life.