The High Court has unanimously dismissed a legal challenge brought by mining magnate Travers Duncan that aimed at striking down laws protecting previous findings of the NSW Independent Commission Against Corruption (ICAC).

In July 2013 the ICAC found Mr Duncan, a former director of Cascade Coal, engaged in corrupt conduct by concealing the involvement of the Obeid family in a Hunter Valley coal tenement.

Mr Duncan tried to challenge the validity of the findings against him in the New South Wales Supreme Court and failed.

He then took his fight to the High Court, where he challenged a new law introduced by the NSW Government that validated ICAC rulings regarding corrupt conduct before April 15, 2015.

The law was brought in after a successful High Court challenge by prosecutor Margaret Cunneen cast doubt on many of ICAC's previous decisions, including the matter involving Mr Duncan.

Lawyers for Mr Duncan argued the introduction of the law overstepped parliamentary powers and undermined the integrity of the NSW Supreme Court.

However the High Court ruled against that interpretation, thereby upholding the validity of previous ICAC decisions.

Mr Duncan has been ordered to pay court costs.