During Ireland's longest ever criminal trial, two former executives of failed Anglo Irish Bank, John Bowe and Willie McAteer, were also convicted earlier this month on the same charges of defrauding investors, depositors and lenders, reports Reuters.
All pleaded not guilty.
Former Irish Life and Permanent (ILP) finance director Peter Fitzpatrick was acquitted last week.
All four men stood accused of conspiring together, and with others, to mislead investors by setting up a €7.2bn (£5.6bn, $8.2bn) circular transaction scheme between March and September 2008 to bolster Anglo's balance sheet.
The prosecution’s case was that the four men were involved in a setting up the scheme where Anglo lent money to ILP and ILP sent the money back, via their assurance firm Irish Life Assurance, to Anglo.
This allowed Anglo to record the "new money" as customer deposits, which are considered a better measure of a bank's strength than inter-bank loans, reports The Irish Independent.
Green jersey agenda
Lawyers for the accused said during the trial that their motivation in authorising the deal was the 'green jersey' agenda, the financial regulator's request for Irish banks to support one another as the financial crisis worsened.
Irish Life placed the deposits via a non-banking subsidiary in the run-up to Anglo's financial year-end, to allow its rival to categorise them as customer deposits, viewed as more secure, rather than a deposit from another bank.
The verdict was read on day 89 of the trial following almost 62 hours of jury deliberation.
Casey, Bowe, and McAteer will be sentenced on 25 July. The penalty is at the judge's discretion and there is no maximum sentence for the offence.
Anglo, described by Judge Martin Nolan during the 74-day trial as 'probably the most reviled institution in the state', was nationalised months later and put into liquidation in 2013.
Its failure cost taxpayers €30bn, equivalent to around 15% of Ireland's annual economic output and almost half the €64bn Dublin had to pump into its banks to save the entire sector from collapse.
Irish Life and Permanent was broken up during the restructuring of Ireland's financial sector. Its banking arm, permanent tsb, remains under 75% state ownership.