The church agreed to the payment after one day of trial in WA's Supreme Court, Rightside Legal said on Thursday.

Father Bert Adderley, who died in the 1980s without ever being charged, abused many boys in regional WA and Perth, the Victorian law firm said.

Last week's trial ended after the survivor gave evidence about the abuse he suffered.

Lawyer Michael Magazanik said the church failed his client for more than 40 years.

"The Church knew Adderley was a child abuser, but it shifted him from Bunbury to Perth and gave him access to new children and new victims, including my client," Mr Magazanik said in a statement.

"There was no doubt about the abuse, and no doubt about the terrible damage - PTSD, major depressive disorder, and substance abuse issues.

"Yet the Archdiocese of Perth fought him all the way."

According to the Broken Rites Australia group, Adderley had been a lay teacher at the Christian Brothers' Aquinas College in Perth in the 1950s before entering the priesthood.

He served as a priest in the Bunbury diocese from 1959 to 1974 and in the early 1960s he oversaw Catholic education in the diocese.

But in 1965, following complaints about sexual abuse, he was "relegated, out-of-sight", to other parishes.

In a statement, Perth Archbishop Timothy Costelloe said the case highlighted the horror of sexual abuse and the dreadful effects it had on victims.

"I am glad that the survivor of this shocking abuse has had the opportunity to have his story told and believed and has been financially compensated," he said.

Archbishop Costelloe acknowledged that the church had a "deplorable" history of abuse of the young and vulnerable which had been exposed by the Royal Commission into Institutional Responses to Child Sexual Abuse.

"Nothing can justify or cancel out the dreadful mistakes of the past," he said.

"What the Church can do today and into the future is to commit itself to treating those who have been abused with dignity, respect and integrity.

"The Church can and must also take whatever steps are necessary to ensure that, as far as humanly possible, such abuse never again occurs within Catholic settings."

The archbishop said he was "deeply sorry and ashamed" that abuse had been carried out by clergy, religious and lay church workers.

"The most recent media reports suggest that the Church has failed to honour its commitment to treat survivors with respect, compassion and sensitivity," he said.

"To the extent that this is the case, I sincerely apologise."

Australian Associated Press