Last month, it was announced that German economist Klaus Regling would carry out one investigation, with the second report to be published by Central Bank Governor Patrick Honohan.
Mr Lenihan said Max Watson, who has held senior positions at the International Monetary Fund, European Commission and Bank of England, would collaborate with Mr Regling and co-author one report.
The minister had already agreed that an additional expert would be appointed to help Mr Regling complete his report, and Mr Watson's appointment came after a recommendation from the German economist.
The two men worked together previously at the European Commission.
The Central Bank Governor will report on the performance of the financial regulatory system, while the second report will be on the causes of the banking crisis, and the lessons to be learned from it.
These reports are to be delivered by the end of May, and will inform the terms of reference of a Commission of Investigation into the banking crisis.
