A drug trafficking conviction based on the word of an underworld drug cook - paid in exchange for evidence by Victoria Police and Lawyer X Nicola Gobbo - has been quashed.

Victoria's Court of Appeal on Friday ordered Mr Cvetanovski, known as Steve, be acquitted and ordered no new trial.

Mr Cvetanovski, 54, says he feels fantastic and hopes the acquittal marks the end of a traumatic, frustrating and confusing period of his life.

"It's life changing. One chapter closes, another one opens," he said leaving court.

He described it as "distressing beyond explanation" to realise the very basics of procedural fairness had been denied to him by those who swore an oath to uphold the law.

His family stood by when he felt alone, he said, also expressing thanks and gratitude to his lawyers and prosecutors, who had conceded he should be acquitted.

Mr Cvetanovski was freed on bail in May, weeks shy of serving his non-parole period.

At the heart of the conviction and the miscarriage was his once-trusted lawyer, Ms Gobbo.

She not only represented Mr Cvetanovski, but the drug cook known as Mr Cooper who was the key witness against him.

Mr Cvetanovski was charged after the cook's drug lab was uncovered by police - after a tip-off from Ms Gobbo - in 2006.

Earlier this month chief crown prosecutor Brendan Kissane QC conceded there had been a failure to disclose the extent of payments made to the drug cook by Victoria Police and Ms Gobbo.

Appeal Court President Chris Maxwell said Mr Cvetanovski had no idea at the time that his lawyer was a registered police informer or persuaded Mr Cooper to co-operate with police to incriminate him.

In exchange for the cook's evidence Victoria Police was paying him $240-a-month into his prison canteen account, as well as a lump sum payment.

Between 2003 and 2012 the cook received almost $20,000. His evidence was used against more than 20 people, including drug kingpin Tony Mokbel.

While the payments were raised at a trial, the extent of the financial support was never revealed and the jury that convicted Mr Cvetanovski was not able to properly assess the cook's credibility, Justice Maxwell said.

"We are satisfied that the Crown's concessions are properly made, that the appeal should be allowed, the conviction quashed and a verdict of acquittal entered," Justice Chris Maxwell said on Friday.

Former top prosecutor John Champion - now a Supreme Court Justice - wrote in a 2016 briefing that without Mr Cooper there would likely have been no case against Mr Cvetanovski.

Last year Faruk Orman was acquitted of murder after the court found Ms Gobbo's involvement in his conviction caused a substantial miscarriage of justice.

There are eight other gangland figures appealing convictions based on Ms Gobbo's informing, including Mokbel and tomato tin ecstasy import masterminds Pasquale Barbaro and Rob Karam.

Australian Associated Press