The 41-year-old southern NSW man, who cannot be named for legal reasons, had previously pleaded guilty to one count of adult maintaining an unlawful sexual relationship with a child and one count of aggravated indecent assault on a child under the age of 16.

The first offence occurred at addresses in NSW, Queensland and Canberra, between March 2013 and November 2013, when the victim was aged 12 to 13 years.

The second offence occurred in southern NSW on September 15, 2017, when the victim was 13.

"The acts of the offender indicate a gross breach of trust given his position in the household," Judge Lerve said during his sentencing remarks in the Wagga District Court on Monday.

"He used the victim in count one essentially as his sexual plaything while apparently being totally and utterly indifferent about his position as her stepfather, her age, the short and long-term effects of his offending conduct on his victim or the utterly inappropriate nature of the relationship that he was continuing.

"In respect of the second count, he took advantage of being alone with the victim in a moving motor vehicle, again indifferent to the position of trust in which he was."

Judge Lerve said no evidence was given by or called on behalf of the man during an earlier sentencing hearing.

However, there were a number of written submissions tendered to the court.

In a report, psychologist John Machlin wrote that the offender "acknowledged the offences in a contrite manner and appearing to appreciate the gravity of his conduct".

Judge Lerve said he was prepared to accept the man was remorseful.

On the count of aggravated sexual assault, the man was jailed with a non-parole period of 14 months, with an additional five-month parole period.

For the charge of maintaining an unlawful relationship with a child, the man was sentenced to a non-parole period of nine years and nine months, followed by a parole period of three years and nine months.

"The total effective sentence is one of 14 years' imprisonment with time in actual custody before being eligible for release to parole of 10 years, three months," Judge Lerve said.