Cameron Flynn Tully, 41, was locked up for sex offences against eight girls who attended his parents' farm, Hillview, in West Belconnen in the 1990s and early 2000s.

The children, who were then aged 7 to 13, gave evidence they were abused at various locations on the farm, including a shearing shed, a bathroom, and his bedroom.

Tully was found guilty on most of the 23 charges brought against him when he faced trial in the ACT Supreme Court in mid-2014.

Justice John Burns sentenced him to 14 years and six months behind bars, with a non-parole period of nine years.

Tully has continued to maintain his innocence and last year appealed against his convictions, in the ACT Court of Appeal.

In February, the court set aside convictions for four offences committed against the same complainant, finding they were unsafe and unsatisfactory because there was not enough evidence to prove the girl's age at the time.

Those charges alleged the girl was under 10 at the time, meaning prosecutors had to prove her age beyond reasonable doubt.

However, evidence at trial raised the possibility she was older than 10.

The Court of Appeal also found the jury may have misunderstood the judge's directions telling them how they should deal with the complainant's age.

That forced the higher court to enter not guilty verdicts on the four counts.

Chief Justice Helen Murrell, Justice Hilary Penfold and Justice Anthony North on Wednesday handed down their decision on how much time should be cut from Tully's sentence as a result of the appeal.

They resentenced Tully to 12 years' imprisonment, with a non-parole period of seven years and three months.

He will be eligible for release in June 2021.