The European Court of Justice in Luxembourg has approved the EU's permanent bailout fund, the European Stability Mechanism.
The ruling was delivered this morning by President of the Court Vassilios Skouris.
It stemmed from a case taken by Independent TD Thomas Pringle in the Irish courts.
Speaking after the ruling, Mr Pringle expressed his disappointment, but said he was satisfied that the ESM had been legally tested.
The TD said he was concerned about the cost of undertaking the legal action, but felt it was vitally important to take the case.
He said it would now be up to the Supreme Court to decide on costs.
The case is expected to be returned to the courts in the coming weeks.
Last month, under accelerated or fast-track procedures, all 27 judges of the ECJ participated in an oral hearing.
It was the first time this happened on a case referred by a national court.
Senior Counsel for Mr Pringle, John Rogers, argued that EU institutions and member states had engaged in mis- characterisation and distortion when creating the ESM and breached EU law.
Senior Counsel for Ireland Michael Cush rejected this, claiming the decisions creating the ESM were fully compatible with EU treaties.
This contention was supported by other member states, such as Germany, and the European Commission.