Acting Justice Peter Berman on Friday sentenced 26-year-old Lwen Pah Eh to two years and three months in jail after he previously pleaded guilty to persistent sexual abuse of a child.

The judge set a non-parole period of one year and three months.

The ACT Supreme Court found Pah Eh had "taken advantage" of a 15-year-old girl multiple times between July and November 2021.

Acting Justice Berman described the man's behaviour, which included forcing her first kiss and first sexual experience, as "seriously criminal".

Pah Eh had made the child an "empty promise" in saying he would not try anything sexual if she snuck out of her parent's home to see him, but continued to rape the victim each time.

"Telling her because they had already had sex that they should be together because 'it was less shameful that way' was an act of manipulation," Acting Justice Berman said.

"As was convincing her what they were doing was normal."

Since the victim agreed to meet Pah Eh in secret against her parents' wishes, Acting Justice Berman said children were "often not in the best position to decide what is best for them".

The judge said there was an obvious power imbalance between the "schoolgirl", and Pah Eh, an adult with a job and a car.

He also found the victim's "unwillingness" during the abuse was largely irrelevant to Pah Eh and noted the crimes were carried out in the middle of the night, while they were alone in isolated locations.

Acting Justice Berman said the victim felt "shattered and worthless".

"Children must be protected from themselves," he said.

"I have no doubt she grieves for what he did."

The judge said Pah Eh was born and raised in a refugee camp, where it was common for 15-year-olds to be married.

He said the offender's childhood experiences were "different" from what was considered appropriate and lawful in Australia, adding Pah Eh did not have parents from a young age to provide "moral instruction".

"[Pah Eh] was told by an older friend that he should keep going if [a girl] says no," Acting Justice Berman said.

The judge further found Pah Eh, described as "naive and vulnerable" by a psychologist, did not have true remorse for his crimes against the child.

When the offender was previously asked what he would say to the victim, Pah Eh said: "I'm sorry for everything, this mess."

The judge said Pah Eh was referring to himself not being able to socialise in the community.

"It falls short of an acceptance of responsibility ... and complete understanding of the harm he's caused," he said.

Acting Justice Berman said full-time imprisonment was the only appropriate sentence and accounted for the 22 days Pah Eh had already spent in custody after his arrest.

Pah Eh was on Friday supported by four people, who heard he would only be eligible for parole in May 2025.