Falciani, who worked as an IT specialist with HSBC, was convicted of industrial espionage by a federal court in the southern Swiss town of
Bellinzona on Friday, the ATS news agency reported.
The 43-year-old French-Italian national refused to travel to Switzerland to appear at trial.
Falciani can appeal his conviction at Switzerland's highest court, but he will not serve any prison time in the federation so long as he remains in
France, which does not extradite its citizens.
The former HSBC employee leaked a cache of documents allegedly indicating the bank's Swiss private banking arm helped more than 120,000 clients hide 180.6 billion euros ($205.4 billion) from tax authorities.
Falciani has been celebrated as a whistleblower by some, but Swiss authorities claimed he was motivated by money, citing evidence that he wanted to sell the data he stole.
Falciani has denied that he was only seeking financial gain, insisting he had wanted to expose how banks support tax evasion and money laundering.
Prosecutor Carlo Bulletti had sought a six-year prison term, while defence lawyer Marc Henzelin asked for a suspended sentence.
Responding to news of the sentence, Falciani told Le Matin newspaper that it was "ridiculous" that the court did not recognize him as a whistleblower.
The fact that the court could only find him guilty of industrial espionage showed the case was not serious, he said, the daily reported online on Saturday.
Falciani said he would not appeal the case "because I give no legitimacy to Bellinzona".
He added that he plans to continue his fight against the opacity of financial transactions.
"Switzerland, like Luxembourg, is protecting people who are not very respectable."
Masses of data stolen
While working at HSBC's Geneva offices in 2008, Falciani made off with material estimated by prosecutors as amounting to more than 76 gigabytes of raw data, capable of filling 5,300 large binders.
After taking the data, he first went to Lebanon with an associate, where the two reportedly tried to sell the material, unsuccessfully.
According to prosecutors, it was only after his plan to cash in on the data fell flat, that Falciani contacted European tax authorities, adopting the
mantle of whistleblower.
He returned to Geneva in 2008, was arrested by Swiss Federal police and questioned for a few hours before being released on the promise that he would return the next day for further questioning.
Instead, he fled by car to France with his family, and in the years since the contents of his leaked material have had ripple effects across the globe.
According to the International Consortium of Investigative Journalists, which published a detailed report of the affair, Falciani assumed a fake
identity and contacted French authorities before ultimately handing over an encrypted list of major HSBC clients based in France committing tax evasion.
The report from the consortium said HSBC also advised convicted drug dealers on how to launder money.
As part of a deal to close a case opened by Swiss prosecutors, HSBC paid a penalty of 40 million francs ($39 million).
Switzerland has pursued Falciani since he ran off, at times straining bilateral relations with France.
At the trial, Falciani's lawyer sought to highlight an irony in the Swiss prosecution, noting that the federation was committed to punishing Falciani
even as it was in the process of dismantling its banking secrecy practices which for decades allowed foreign clients to hide billions from the taxman back home.