Luxembourg's highest court scrapped an appeal court's six-month suspended sentence and 1,500-euro fine on former PricewaterhouseCoopers (PwC) auditor Deltour, recognising his status as a whistleblower as the lower court had already done.
But the top court ordered a new trial with different judges because Deltour took PwC internal training documents, even though he did not pass them on to anybody.
It also rejected the appeal of another French national, Raphaël Halet, who leaked more PwC documents to the French TV programme Cash Investigation after hearing that Deltour had done so, finding that he had not provided any new information that contributed to the tax evasion debate and upheld his 1,000-euro fine.
the court confirmed the acquittal of Cash Investigation journalist Edouard Perrin, who received the documents from both men.
Deltour hailed a "great victory" in his case but said he was disappointed about the ruling on Halet, with whom he expressed his "total solidarity".
European directive followed revelations
The leaks in 2012 revealed that 340 companies had benefited from "tax rulings", commitments by the country's authorities that they would pay as little as one percent tax if they registered in the Grand Duchy, while current European Commission president Jean-Claude-Juncker was prime minister.
The story hit international headlines in 2014 when the International Consortium of Investigative Journalists (ICIJ) shared 28,000 documents with international media in the Luxleaks dump.
Luxleaks, which was followed by other tax evasion revelations in the Panama and Paradise Papers, led to a European directive ordering member states to share information on secret deals and Deltour was named the European parliament's citizen of the year in 2015.
Ruling on Halet house search next month
On 6 February a French court will rule on the validity of a 2014 order by a court in Metz, eastern France, which authorised a search of Halet's home to find out if he was Perrin's source.
Prosecutors have found that it was prejudicial to the confidentiality of journalists' sources "without legitimate cause".