A former chaplain at a Perth girls' school has been found guilty of possessing pornographic images and videos of young girls.

It was the second time Matthew David O'Meara stood trial accused of possessing the material while he was the chaplain at Perth College in 2010.

Last year his trial ended in a hung jury.

However, after deliberating for more than three hours on Monday, a District Court jury found him guilty of all four charges against him.

During the first trial, O'Meara denied downloading child pornography from the internet.

The images were on two thumb drives; one was found in a colleague's classroom and the other in the pocket of O'Meara's trousers.

He testified he found the second thumb drive in a staff area of the chapel and intended to take it to lost property but police arrived at the school to interview him.

O'Meara's wife wept as the verdicts were delivered.

Outside court, his lawyer David Manera said the former chaplain was devastated with the outcome.

The judge released O'Meara on bail but told him an immediate term of imprisonment was almost inevitable.

O'Meara declined to answer reporters' questions as he left court.

He will be sentenced on Thursday.