Lawyers for Mayo native, former solicitor Michael Lynn have said that he has instructed them to file an appeal immediately against his conviction and sentence.
His lawyers said they were also calling for the Oireachtas to set up a tribunal of inquiry into banking in Ireland.
Yesterday, Mr Lynn was jailed for five-and-a-half years for stealing just over €18m from financial institutions in 2006 and 2007.
He had pleaded not guilty to 21 counts of theft amounting to almost €30m from a number of financial institutions between October 2006 and April 2007 but was convicted of ten offences after a trial last year.
The court heard he took out multiple mortgages on the same properties from different financial institutions who did not know other banks were also providing finance.
According to RTE, Solicitor Ciarán Mulholland from law firm Mulholland Law issued a statement yesterday evening criticising what he described as "an incredibly aggressive prosecution" against his client.
Mr Mulholland said neither of the juries in the two trials were able to reach a verdict on the majority of the counts against Lynn.
He described the case as unprecedented and highly complex for all the parties involved and said it was "staggering" that the actual loss to the banks still could not be quantified.
He also set out a number of criticisms of the prosecution of his client and the actions of bankers, gardaí, lawyers and the Department of Justice.
Mr Mulholland added that the case continued to raise more questions than answers and said the majority of the questions were directed at the banking institutions.
He said they were calling on the Oireachtas to establish a tribunal of inquiry to "properly investigate" the "systemic flaws of banking in Ireland", which he said was clearly of "significant public importance".