Developer Paddy McKillen won a legal challenge today to stop NAMA taking control of €2.1bn in loans.
The Supreme Court overturned an earlier ruling that the National Asset Management Agency (NAMA) could acquire the loans owed by the property investor's companies.
The country's top seven judges found the initial decision by NAMA to take the loans was invalid as it was taken by officers prior to the agency coming into existence.
Chief Justice Mr Justice John L. Murray told the packed courtroom the decision taken by an interim team had no legal effect.
"Consequently, NAMA has made no decision to acquire the appellants' loans," he said.
"The appellants are, therefore, entitled to a declaration to that effect."
The successful developer, who has 62 properties including shopping centres, hotels and offices, has extensive loans with both state-owned Anglo Irish Bank and the Bank of Ireland.
His barristers argued that most of his loans were performing remarkably well in the current climate and almost all properties are occupied by tenants.
Attorney General Paul Gallagher, who represented the State, said the acquisition of loans was necessary because of the extent of exposure to the financial institutions participating in NAMA.
But the judges found an interim management team decided on December 11 and 14 2009 to acquire Mr McKillen's loans - 10 days before NAMA was established and the National Asset Management Agency Act came into force.
The Chief Justice said: "The court does not agree that the question of whether NAMA has made a decision is a purely technical and formal one. A decision to acquire eligible assets is an essential step in the statutory process."
Finance Minister Brian Lenihan said he needed to study the judgment before making a comment.
"He may have won on a technical issue but lost on the merits," he said.
A spokeswoman for NAMA said it was not yet commenting on the outcome of the case.
Mr McKillen was not in court for the judgment, which also found the agency had not breached the terms of a European Commission decision permitting the state to grant aid under the Nama Act 2009.
The ruling means the board of NAMA could make an official, valid decision to acquire Mr McKillen's loans and start the process of acquiring them again.
Frank Daly, chairman of NAMA, said the outcome of the hearing was obviously a disappointment especially as the earlier High Court judgment found comprehensively in favour of NAMA.
"However, it is important to note that the decision relates specifically to the particular case as presented by Mr McKillen and does not have implications for other acquisitions now completed by NAMA," he said.
"It is also important to note that the Supreme Court has ruled firmly that NAMA did not breach state aid rules.
"We will study the ruling carefully over the coming days and reflect on the options ahead."
Mr Daly said it was worth remembering that NAMA was established as an emergency response to an unprecedented threat to the country's banking system and its wider economy.
"In that context, our purpose at all times has been and remains to work as efficiently and objectively and fairly as possible in order to deal with the onerous responsibilities that were entrusted to us," he added.
The case was adjourned until next Wednesday when the court will hear submissions on what will happen to the other issues in Mr McKillen's appeal which included the right to fair procedures, constitutional issues and whether NAMA failed to take into account relevant considerations when deciding to acquire the loans.