In April last year an arbitration panel employed by two parties to settle their differences found that the French firm had wrongly paid commissions to intermediaries to secure a huge warship contract.
Thales appealed the private panel's decision in a civil court, but on Thursday its complaint was thrown out, leaving it facing a bill of at least $591 million plus interest and legal fees.
The French defence and electronics firm signed the original contract to supply Taiwan with six Horizon-class frigates in 1991. The deal specifically excluded the payment of sweeteners to go-betweens.
Thales can still appeal the latest ruling – which was based not on a re-examination of the case itself but on the conduct of the arbitration – in France's top appeal court, the Court of Cassation.
It was not immediately clear whether it would do so.