It was brought by Green Party TD, Patrick Costello.
The High Court's dismissed a challenge by a Green Party TD to an international trade deal between the EU and Canada.
Patrick Costello had challenged the constitutionality of the agreement, known as CETA.
He says he will take time to consider the judgement and possible next steps.
Eamonn Torsney reports:
"Green Party TD Patrick Costello had argued that ratification of CETA would have a chilling effect on the state's willingness to introduce regulations regarding the environment.
He also questioned how an 'investor court service' could be created without the agreement being put to a referendum.
In her judgment, Ms Justice Butler said the Deputy Costello had not established that ratification of CETA in the manner proposed would be clearly unconstitutional.
Reacting to the decision Patrick Costello says he will have to take time to study the judgement before deciding whether to appeal it.
In a statement he says there are significant issues in the case that need to be considered further and would benefit from being clarified by the Supreme Court."
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