Brett John Callaghan, 39, pleaded guilty to a series of charges, including two aggravated counts of having sexual intercourse with a child and supplying a prohibited drug to a child.

Judge Robert Sutherland in the NSW District Court on Friday sentenced him to a non-parole period of nine years, and a maximum term of 12.

The judge said the predatory and opportunistic behaviour and the abduction of a child was "undoubtedly a parent's worst nightmare".

Callaghan acknowledged in a letter to the court that the harm he caused "probably ruined her life".

The terrifying ordeal for the girl on April 28, 2020 was read out by the judge.

Following a day spent shopping with a friend at Hornsby Westfield she waited for another in Thornleigh skate park.

Five minutes after her friend departed Callaghan approached her at 3.34pm and offered to charge her mobile phone at his house.

She initially declined but was given the impression he knew her friend and told her they would only be "10 minutes" before dropping her back.

He pointed to another young child seated in his car in reassurance she would not be hurt.

They drove to a semi-rural Dural property where his parents lived in the main house and he resided in a granny flat out the back.

She reminded him she needed to be at Hornsby station before 4.30pm to be picked up by her mother.

He then offered her "the good stuff" in an ice pipe and two puffs later she felt uneasy, tired, hot and cold, and became worried by his behaviour.

She ran down the 200m-long driveway screaming and a neighbour came out but Callaghan drove up alongside and said he would drive her home.

At some stage he pulled over saying he was waiting for a friend and she left the car so stressed and frustrated she punched a tree.

She ran away but "could not see anything in sight" and returned.

"I will do anything just please drive me home now and get whatever you need to get later,"' she said.

He then demanded a sexual favour before he sought assistance from a nearby resident more than three hours later as his car battery was flat.

By this stage his victim said she felt stuck and gave up trying to go home.

When they arrived back in his bedroom he sexually penetrated the girl who later said she was in "so much pain," and that she felt powerless and like crying.

When police arrived about 1am she was told to hide under a blanket but he eventually admitted she was there, saying "I didn't know she was 13 she looks 19 easy".

Callaghan wrote a letter to the court about his directionless and drug-addicted life after his dreams of becoming an Olympic swimmer were dashed at Commonwealth Games trials.

After failing a drug-test at 17 and being kicked off the team, he began long-standing battles with alcohol and drug abuse.

A psychiatric assessment noted a number of disorders including ADHD and the possible presence of pedophilic disorder.

In an earlier sentence hearing, the girl's mother detailed the "catastrophic" impact the "abhorrent" attack had upon her.

She said her personality had fundamentally changed and she no longer smiles in photos.

Callaghan is first eligible for parole on April 28, 2029.

Australian Associated Press