Ian Bailey faces substantial legal costs running into millions of euro after a ruling from the Court of Appeal.
He lost his appeal against orders requiring him to pay the costs of his failed action for damages over the conduct of the garda investigation into the murder of French woman, Sophie Toscan du Plantier, in 1996.
The Court of Appeal gave its ruling on costs following its judgment last month, which overturned its own earlier decision to allow a retrial of one part of Mr Bailey's action, meaning he lost his entire appeal.
Mr Bailey had appealed against the dismissal of his case in the High Court where a jury rejected his claim that three gardaí had conspired to frame him for Ms Toscan du Plantier's murder.
Mr Bailey's Senior Counsel, Martin Giblin, said the "highly unusual" circumstances of the case were grounds for the Appeal Court to depart from the normal rule that costs go to the winning party.
However the Appeal Court ruled against him.
Mr Bailey's lawyers have appealed separately to a French court over a decision by the French authorities to charge him with Ms Toscan du Plantier's murder.
He has always denied any involvement.
