Grocon Victoria Street Pty Ltd, an subsidiary of the construction and building giant, had pleaded guilty to failing to ensure a safe workplace in March last year when the wall came down at a vacant Swanston Street site earmarked for redevelopment.

Teenage siblings Alexander and Bridget Jones, of Melbourne, and Frenchwoman Marie-Faith Fiawoo, 33, were killed when a 15-metre long section of the freestanding brick wall and attached advertising hoarding were pulled down in strong winds.

But Magistrate Charlie Rozencwajg found every member of the public was put at risk because of the company's failure to ensure its subcontractor, Aussie Signs, had taken steps to ensure the hoarding was safe.

He noted how the wall was in such a dire condition, however, that it may have crumbled on to the footpath even without the attached hoarding.

"That clearly makes it a serious offence," he told the Melbourne Magistrates Court on Friday.

"This represents a significant factor in the company's failure."

He imposed a $250,000 fine and ordered Grocon to pay legal costs. The fine was within the range that Grocon's legal team had earlier suggested would reflect the seriousness of the safety breach.

He said the early guilty plea, which helps victims achieve closure, and Grocon's "sincere and appropriate" apology were factors in reducing the size of the fine. The guilty plea saw the company admit fault only in assessing the risk, not in causing the three deaths.

Grocon and the Victorian WorkCover Authority declined to comment outside court after the sentencing.

But Grocon chairman Daniel Grollo later released a statement expressing his deep regret over the fatalities.

"In whatever small way, we hope that the timely conclusion of the proceedings today assists the families and friends affected by this tragedy," Mr Grollo said.

"Our thoughts and sympathies remain with all of those affected by the loss of these three young lives."

The CFMEU said the fine was simply a slap on the wrist for such a large building company.

"We are all asking the same question: what is a life worth?" CFMEU state secretary John Setka said in a statement.

"This tragedy, which robbed three young people of their future and scarred so many other lives, could have been avoided. It is a shocking reminder of the need to fight every day to make the construction industry safe."

A coronial inquest into the three deaths is expected at a later date. Aussie Signs has not yet indicated its plea and is still awaiting a possible trial.

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