Antoine Deltour, 31, Raphaël Halet, 40, were found guilty of leaking documents belonging to their former employer Price Waterhouse Coopers but journalist Edouard Perrin, who broke the story in the French TV programme Cash Investigation, was found not guilty.
Deltour was given a 12-month suspended prison sentence and a 1,500-euro fine, while Halet was given a nine-month suspended sentence and a 1,000-euro fine.
The 30,000 pages of confidential documents they passed to the press revealed that multinationals, including Amazon, Apple, Ikea, Pepsi, McDonald's and BNP-Paribas, negotiated "tax rulings" that allowed them to pay as little as one percent tax if they registered in the Grand Duchy.
European Commission President Jean-Claude Juncker was Luxembourg's prime minister at the time.
Defendants to fight on for other whistleblowers
Luxembourg's legal authorities charged Deltour and Halet with stealing documents from the accounting firm's database, revealing business secrets, violation of professional secrecy and money-laundering, which could have meant 10 years in jail.
Perrin, who was in the US at the time the verdict was read, was charged with complicity.
Prosecutors called for 18-month prison sentences and an unspecified fine.
So the sentence was relatively lenient but not lenient enough for the defendants and their lawyers.
Ahead of the verdict they said they would appeal even if just a one-euro fine was imposed, because they wanted to establish jurisprudence for future whistleblowers.
Scandal put pressure on court
The leak hit international headlines in 2014 when International Consortium of Investigative Journalists (ICIJ) shared 28,000 documents with international media in the Luxleaks dump.
The uproar created by the revelations put pressure on governments to chase up tax-dodgers and on Luxembourg to review the issuing of tax rulings.
French Finance Minister Michel Sapin, who has netted billions from tax-dodgers largely thanks to whistleblowers, declared his support for Deltour in front of the French parliament in April, saying that his action had "ended the opacity that prevents European countries from knowing the tax situation certain big companies in Luxembourg".
The European parliament set up a special committee to look into tax evasion following the leaks and Deltour was invited to address it in June 2015.
NGOs, including Oxfam France, campaigned for acquittal and demonstrated in front of the court and Luxembourg's embassy in Paris on Wednesday.