The Labour Party leader has said the Comptroller and Auditor General's report effectively confirms the Government has "grossly mishandled" the Institutions Redress Scheme for victims of childhood abuse.
Describing the Government's record on the issue as "reckless, profligate and irresponsible", Mr Pat Rabbitte said it was clear the total liability arising from the scheme could exceed a billion euro.
He also said it was clear the religious orders were allowed to cap their contribution on the basis of a "ludicrously small" estimate of the total liability.
Mr Rabbitte said the Department of Education appeared to have conducted the talks with the congregations without ever seeking to ascertain their ability to pay.
"The Attorney General only sought outside legal opinion on the entire issue a matter of days before it was agreed by the outgoing Government, and on the basis of that advice the Government was warned that the €128 million agreed as the congregations' contribution was unlikely to be sufficient," he said.
"The Government was also told before they agreed the deal that it contained no mechanism whatever for increasing the contribution from the congregations if the number of cases increased greatly.
"This is proof, if proof were needed, that the last Government behaved in an entirely reckless and profligate manner in relation to this deal. The public has a right to know what really motivated this rushed and irresponsible arrangement," Mr Rabbitte said.
Fine Gael's education spokeswoman, Ms Olwyn Enright, said the C&AG's report proved the Government "totally botched" negotiations on the deal with the religious orders.
She said State exposure to potentially enormous liability was clearly not a factor considered by ministers and it is evident that crucial legal advice was not obtained.
"It is clear from C&AG's report that the Government failed utterly to adopt a robust and informed stance in the negotiations on these two issues."
Ms Enright said that secret negotiations along with the lack of contemporaneous notes, the Government approval of the arrangement based on an oral report and the drafting of a retrospective memorandum added up to a "damning indictment" of the manner in which the Government reached the deal.