Denis O'Brien has lost his Supreme Court challenge to a High Court ruling relating to a key witness in the Moriarty Tribunal.
The businessman claimed he was denied his right to fair procedure because he believed his lawyers were not given enough time for a witness cross-examination.
Professor Michael Anderson, a Danish telecommunications expert, was one of many witnesses called to give evidence as part of the investigation into the awarding of a mobile phone licence to Esat Digifone in the 1990s.
Denis O'Brien claimed his evidence was crucial but argued his lawyers were unfairly restricted in the questions they could ask in their cross-examination and the time they were given to ask them.
In 2011, the High Court rejected his claim that he was denied his right to fair procedures and that decision was upheld by five Supreme Court judges today.
Professor Anderson had alleged that some of the tribunal lawyers were biased against Mr O'Brien's company and Chief Justice Susan Denham found it to be a central factor that his evidence was favourable to the businessman.
She also rejected Denis O'Brien's argument that his rights were breached when a six-hour limit was put on his time for cross-examination.