The Waigani National Court convicted him after the court was satisfied beyond reasonable doubt that he did sexually penetrate his daughter following a trial.
He will return to court today where the court will hear submissions on sentence.
Presiding judge, Justice Nicholas Kirriwom in his ruling on verdict said the father lied to the court that he only sexually touched his daughter.
He said there was no logic that a sensible person would believe the father would have picked her up from school in three different occasions just to fondle her.
The victim was a month shy of turning 13 years old when he first sexually assaulted her in August 2012. That continued in September and November of 2012.
He sexually assaulted her at a relative's house at the PNGEI College, inside a tinted cab at Five-Mile and at the family house at Gerehu on the three occasions.
He threatened her with a kitchen knife before violating her.
She was then in grade 6 and was the youngest of his three children. He and his wife took her in after she could not give him more children.
A medical report conducted by a gynaecologist at the Vunapope Hospital in Rabaul in January of 2014 revealed she contracted an STI and received treatment.
Her mother took her to the hospital after she noticed foul body odour from the girl. Her behaviour both at home and school also changed and she told the mother everything after the mother asked.
The father of three children had an unhappy marriage of 18 years and he told the court that it was because his wife was the more prominent figure at home.
His wife told the court from the witness box that he was a good father but changed after he lost his job in 2009. He would go around borrowing money and ran away from home just to avoid those he got money from.
After his conviction, he apologised to the court, his wife and children for his actions.
He has been in custody since 2013. He was remanded at Kerevat before being transferred to Bomana in Port Moresby for his trial. He will be sentence at at later date.