The offender, 64, was sentenced to more than four years imprisonment for sexually abusing the child in the 1990s, when she was aged between 10 and 11.

He had entered into a relationship with her mother, and the pair later married.

Much of the abuse took place in two family homes, and was described as a "significant breach of trust".

He forced the child to touch him, rubbed himself against her while she sat on his lap, and indecently touched her.

One of the indecent acts took place in the water at Point Hut crossing.

The court heard the crimes had a "devastating" impact on the child's life. She later began to abuse alcohol, required psychological help, and has suffered problems with intimate relationships.

At the time of the abuse, she was frightened and confused, and didn't know who to tell, or what to say.

But she made reports to a relative and a teacher years later, before making a formal complaint to police last year.

The stepfather was found guilty in the ACT Supreme Court, but still continues to deny the offences, and shows no remorse, insight into his offending, or empathy with the victim.

He believes the case is a "fabricated conspiracy against him".

The court heard he is also being sentenced for offences against two other girls, a process that began on Monday before being adjourned until next month.

Acting Justice Linda Ashford said she was concerned by his outright denial and his opposition to rehabilitation programs.

She said it was important to send a message that such crimes would attract "stern punishment".

"Most of these events took place in the home, a place where she was entitled to feel safe," she said.

"As a step-parent, his actions are a significant breach of trust to a young child."

The man was sentenced to four years and three months imprisonment, with a non-parole period of two years and six months.

He has served four months already, meaning he will be eligible for release in September 2017.