Mining billionaire Clive Palmer has failed in a last-ditch effort to classify himself as a foreign investor so he could sue Australia for almost $300 billion.

Palmer will instead have to pay the Commonwealth $13 million in court costs after the Swiss Federal Supreme Court on Wednesday upheld an international tribunal's finding from last year, bringing to an end a years-long legal saga.

The case centred around Palmer’s Singapore-based company, Zeph Investments, which had sued Australia for $296 billion in damages after a mining proposal in Western Australia was blocked under emergency legislation in 2020.

Palmer, a former Australian federal politician, argued the government had breached the ASEAN-Australia-New Zealand Free Trade Agreement in scuttling the proposed iron ore project in the Pilbara.

Attorney-General Michelle Rowland said the Albanese government had vigorously defended the claim and lamented the time and money the Commonwealth had spent arguing the case.

“The Swiss Federal Supreme Court has confirmed that Mr Palmer is not a ‘foreign investor’ and is not entitled to any protections under Australia’s free trade and investment agreements,” Rowland said in a statement.

“Australia had to spend more than three years and $13 million defending a legal claim that tried to put everyday Australians on the hook for $300 billion.”

The Permanent Court of Arbitration, established under international treaties, had previously dismissed Palmer’s claim, saying the dispute was between a national government and one of its citizens – and therefore not under the court’s jurisdiction.

That came after Palmer’s failed High Court challenge over the validity of the Western Australian emergency legislation, in a move that could have bankrupted the state.

Palmer – Australia’s fifth-richest person and worth an estimated $20 billion – claimed the legislation was “akin to the actions of a banana republic” in a notice of arbitration to the international tribunal after the High Court rejected the challenge.

He told The Australian Financial Review in 2024: “It’s quite allowed under the treaty for Australians to own offshore companies that are operational, and they still get treaty protection. So we employ up there [in Singapore] about 600 people, and we have done for a number of years.”

Palmer has launched a similar action against the Commonwealth for a project in Queensland, worth $40 billion in damages, and is bankrolling a second class action over COVID vaccine mandates in the state. He lost a “flimsy” case against a former Australian Securities and Investments Commission chair last month.

The mining magnate told the National Press Club last year that if he was successful in his lawsuit, he would spend the money better than the federal government.

Palmer’s Trumpet of Patriots political party spent more than $50 million on advertising in the 2025 election but did not win any seats.

Palmer was contacted for comment.