Former chief executive officer of Irish Life and Permanent Denis Casey has been found guilty of a €7.2 billion conspiracy to defraud.
His conviction brings to an end the country's longest running criminal trial, after 89 days.
Casey will be sentenced on 25 July, along with former Anglo Irish Bank executives, John Bowe and Willie McAteer, who were found guilty of the same offence last week.
IL&P's former Finance Director, Peter Fitzpatrick was found not guilty.
The 11 jurors began deliberating on 17 May. In total they were deliberating for almost 62 hours, the longest jury deliberations ever.
The prosecution case was that the men had agreed a scheme in which billions of euro went round in a circle between Anglo Irish Bank and IL&P and was "dressed up" as corporate deposits of €7.2bn in Anglo's end of year accounts, in order to make Anglo Irish Bank look much healthier than it was.
Casey was found guilty by a majority verdict of ten to one.
Casey's lawyers had argued that he was influenced by the "green jersey agenda" - whereby Irish banks were encouraged by the regulatory authorities to help each other out.
But the judge ruled that the attitude of the authorities could provide mitigation but could not provide a defence.
The court was told by Casey's lawyers that he had been duped - that he did not intend to mislead anyone and that he did not know how Anglo would treat the money in its end of year figures.
The jury also heard evidence of a telephone conversation in September 2008, between Anglo Irish Bank's then Chief Executive, David Drumm and Anglo's Head of Capital markets, John Bowe in which Mr Drumm spoke about the "six billion fixes which Mr f***ing Denis confirmed for me this morning". Mr Drumm and Mr Bowe agreed that even with this, the bank was still in a hole.