The kingpin fronted the Victorian Court of Appeal on Tuesday for the first day of his long-awaited appeal against drug trafficking and importation convictions.
Mokbel, who was released on bail in April, claims he suffered a miscarriage of justice because he was represented by Ms Gobbo while she was a police informer.
The then-barrister was registered as a Victoria Police informer from 2005 to 2009 and was acting as Mokbel's lawyer for four years before he fled to Greece in 2006.
She continued to advise him when he was extradited to Melbourne in 2008.
Mokbel pleaded guilty to two counts of trafficking a drug of dependence for trafficking MDMA and methamphetamine in April 2011 after striking a deal with prosecutors.
He did not find out about Ms Gobbo's status as an informer until the High Court lifted gag orders in 2018.
In pre-appeal rulings, NSW Supreme Court Justice Elizabeth Fullerton found former director of public prosecutions and current Victorian judge John Champion was told in June 2012 that Ms Gobbo was a registered informer.
Justice Fullerton was also satisfied Justice Champion knew Victoria Police held concerns about the integrity of Ms Gobbo's clients' convictions at the time of the June meeting.
But Justice Fullerton ruled it was only after another meeting in September 2012 that Justice Champion had an obligation to disclose Ms Gobbo's status to the court.
On Tuesday, Mokbel's barrister Julie Condon KC argued Justice Fullerton should have found Justice Champion breached his duty of disclosure as early as June 1, 2012.
"The director ... was obliged to at the very least notify this court that there was a pressing matter, albeit not capable of overt disclosure, that had come into his direct knowledge," Ms Condon told the Court of Appeal.
"It was of such a nature that the director couldn't sit back and do nothing - which is, in effect, what he did."
She noted Mokbel was sentenced on July 3, 2012 and Justice Champion should have approached the sentencing judge and sought a delay while the matter was investigated.
Office of Public Prosecutions' David Glynn argued it was not practical for Justice Champion to seek a delay, saying it would have pushed back Mokbel's sentence for years.
The appeal hearing before justices Stephen McLeish, Maree Kennedy and Stephen Kaye continues.
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