The man, who cannot be named, stood trial this week on allegations he repeatedly had sex with his foster daughter when she was aged 14 and 15, in 2010 and 2011.

The Crown argued the girl was infatuated with the man, and the pair were allegedly having sex on a daily basis on one point.

She said the man had emotionally blackmailed her, threatening to kill himself if she told anyone.

She also said he had urged her to "deny, deny, deny" if anyone ever asked her about their alleged relationship.

But the father, 35, had fought the charges, maintaining he had never touched or had sex with the girl.

He said he had erectile dysfunction, which did not fit with the girl's claim to police that, on occasions, they had sex for a period of one to two hours.

The girl also failed to make any mention of a mark near his groin area when asked by police.

That was used by the man's barrister James Sabharwal to suggest the pair could not have had sex.

"If she hasn't seen a mark, she hasn't seen this man naked," Mr Sabharwal said.

"And if she hasn't seen this man naked, she hasn't had sex with him."

But Crown prosecutor Anthony Williamson pointed to a large volume of complaint evidence, and the strength and consistency of the girl's evidence, as proof of the truth of her claims.

Mr Williamson said the man had lied to police about the extent of his erectile dysfunction, and had given in to his lusts for the girl.

The jury deliberated for less than a day on Friday before clearing the man on all 12 counts of having sexual intercourse with the girl.

The foster father told police as he was interviewed that the period following the girl's allegations had been horrible.

"It is the reason I am never going to foster or work with young people again because going through something like this is not pleasant," he said.

The man's wife gave evidence in the trial, and then sat in the court to support him.

The trial took roughly four days before Justice Richard Refshauge in the ACT Supreme Court.