The man, who cannot be identified, is now suing solicitor Jason Parkinson for professional negligence, claiming he "spiralled into depression" after signing off on the agreement.

Mr Parkinson, the principal of Canberra firm Porters Lawyers, is defending the claim.

At the commencement of a civil trial on Monday, the plaintiff's barrister, Greg Stretton SC, told the ACT Supreme Court the man had been subjected to abuse that ranged from sexual fondling to rape.

The plaintiff said these acts had been perpetrated by various Marist brothers, including the notorious John "Kostka" Chute, and a teacher named Paul Lyons.

He told the court he clearly remembered the identities of some of the men who had abused him, while he had used old school yearbooks to determine who the others were.

Mr Stretton said the man, who attended the college during the 1980s, had met Mr Parkinson in 2008 and described the horrific things that were done to him.

Mr Parkinson, a former NSW Police detective, now works with victims of institutional sexual abuse and is described on his firm's website as a "leading child abuse lawyer".

According to Mr Stretton, Mr Parkinson agreed to act for the plaintiff and pursue a claim against the Marist brothers.

The barrister told the court that some time later, in March 2010, Mr Parkinson informed the man, "despite his protests", that "he had no other option but to settle".

Mr Stretton said the man had disclosed to a psychiatrist he had also been sexually abused by a family member in 1978, and Mr Parkinson allegedly told the man the psychiatrist's report "mandated settlement".

He also alleged Mr Parkinson had "an apparent obsession" about legal costs and put considerations about those ahead of the plaintiff's interests when he told the man to take the settlement deal.

"The plaintiff caved in to the pressure and the matter was settled for $92,000, of which the plaintiff was to receive approximately $42,000," Mr Stretton told the court.

"As a result of what occurred, the plaintiff felt strongly that he had been the subject of an injustice, and he spiralled into depression."

Mr Stretton said the plaintiff was later given about $27,500 in a second claim in 2017, meaning he received about $69,500.

"Porters' fees were charged at $55,000," he said.

Mr Parkinson's barrister, Dominic Villa SC, said the case would come down to whether Mr Parkinson had acted reasonably in the circumstances at the relevant time.

When Mr Villa cross-examined the plaintiff on Monday afternoon, the man agreed he had been aware that agreeing to a settlement would guarantee him a sum of money, whereas proceeding to a contested hearing in court left open the possibility that he might walk away with nothing.

The trial, before Justice Michael Elkaim, continues.

Our journalists work hard to provide local, up-to-date news to the community. This is how you can continue to access our trusted content: