John Thomas Lawrence, 75, was abused over eight years at the Clontarf and Castledare institutions in Perth in the 1950s.

The Christian Brothers admitted liability on the first day of a recent WA District Court civil trial but sought to minimise Mr Lawrence's compensation on the basis the child migrant from the UK would have had poor economic and educational prospects regardless of the abuse.

At the trial - which was expedited as Mr Lawrence has a shortened life expectancy due to leukaemia, heart disease and diabetes - he testified he was raped multiple times by Brother Lawrence Murphy from the age of nine - first at Castledare three weeks after he arrived.

He had removed his pyjamas after he wet the bed and Brother Murphy took advantage of the situation, telling him to stop crying or he would get "the strap".

Brother Murphy then abused him at Clontarf.

The court heard he would walk through the dormitory at night and pick out boys to take back to his room.

"If I told him to stop, he'd slap me across the face," Mr Lawrence testified.

He also detailed persistent abuse he suffered at the hands of Brothers Francis Marques and Alonzo Angus as well as a lay teacher, Joey Jackson, who made him wear lipstick and a skirt while being violated.

All of the abusers are now dead.

Judge Mark Herron accepted Mr Lawrence's evidence he was threatened by Brother Murphy that he would be beaten if he was not quiet while he was being raped, saying he did not report the abuse because he feared the violence and being accused of lying.

The court heard Mr Lawrence was illiterate when he left Clontarf aged 16 and had suffered "catastrophic" psychiatric harm from the abuse, seeking to end his life dozens of times and struggling to hold down meaningful employment.

Outside court, Mr Lawrence said he could now move on with his life and urged other victims to come forward.

"I'm just glad it got this far after 60-odd years," he told reporters.

"Money is not everything: I'm just glad I told my story."

Mr Lawrence labelled the Christian Brothers "a disgusting mob".

"I just don't know how they get away with it."

His lawyer Mark Magazanic said it was a landmark decision.

The case is the first to go to trial since the state government removed a time limit on child sex abuse survivors taking legal action in 2018.

"It's the first time in Western Australian history that a judge here has passed judgment on what was a complete local disaster," Mr Magazanic said.

"Hundreds of local children were damaged by the abuse in the Christian Brothers orphanages."

Costs are yet to be determined.

Australian Associated Press