The Supreme Court has dismissed the appeal by Denis Casey the former Chief Executive of Irish Life & Permanent against his conviction for a €7bn conspiracy to defraud.
In a unanimous decision five judges of the Supreme Court ruled that Mr Casey was not entitled to a defence of "officially induced error".
The decision was delivered by Mr Justice Peter Charleton.
Casey claimed he should have been allowed to use the role of the Financial Regulator, Central Bank and the Department of Finance as a defence in his trial.
He was found guilty of a conspiracy to defraud and sentenced to two years and nine months in jail in July 2016.
The jury found he conspired with John Bowe and Willie McAteer from Anglo Irish Bank to engage in transactions aimed at fooling people into thinking Anglo had received an extra €7.2bn in customer deposits, as the financial crisis hit in 2008.
Anglo's former boss, David Drumm was convicted of the same offence last year.
Casey argued he authorised IL&P's side of the transactions on the basis that the Financial Regulator was fully aware of them and that they had been encouraged as part of the "green jersey agenda" where Irish banks were to help each other out.
His lawyers said he believed the transactions would be scrutinised before Anglo's year end results were published.
In his judgment, Mr Justice Charleton said that the defence of officially induced error is an exception to the rule and ignorance of the law is no defence.
He said for this defence to succeed the accused must prove that they went in good faith to seek legal advice from an authority.
"It is no enough that an accused give a vague outline to that authority of what he or she proposes," he added.
Mr Justice Charleton said the advice that an action is lawful must be specific, it must be clearly authorised and there must be no deviation from the authorised conduct.
The judge said there was no evidence in the trial that would have enabled the defence of officially induced error to succeed and upheld the judgment of the Court of Appeal.
The court heard that Casey was released from prison in June last year.