The unnamed 45-year-old from Zurich used the social network’s feature to approve of a string of posts attacking the leader of an animal rights group.
It is believed to be the first time a social media user has been punished for just liking something.
According to a court statement, the defendant had accused Erwin Kessler and the animal protection group he heads, Verein gegen Tierfabriken (Against Animal Factories), of racism and anti-Semitism in Facebook posts.
But the court also took issue with the man’s decision to hit the “like” button under several comments from third parties about Kessler that were deemed inflammatory.
The comments were made in 2015 during heated discussions on a range of Facebook groups about which animal welfare groups should be permitted to take part in a large vegan street festival, Swiss daily Tages Anzeiger reported.
Kessler has sued more than a dozen people who took part in those exchanges, a lawyer for one of the defendants, Amr Abdelaziz, told AFP.
Several people have already been convicted in the case, mainly for specific comments they made, but it appears the man convicted Monday was the first to be sanctioned merely for “liking” comments made by others.
In its statement, the court said it did not matter that the comments had not originated from the defendant, whose name was not given.
“By clicking the ‘like’ button, the defendant clearly endorsed the unseemly content and made it his own,” the court statement said.
Kessler had been convicted under Switzerland’s anti-racism law nearly two decades ago, receiving a brief prison sentence for comparing Jewish ritual slaughter methods with Nazi practices.
But the Zurich judge ruled Monday that the defendant had failed to prove that the comments he had “liked” on Facebook were true.
At the same time, by “liking” the comments, the man had disseminated them to his list of Facebook contacts and “thus made them accessible to a large number of people”, the court statement said.
His actions should thus be considered as an “affront to (Kessler’s) honour”, it added.
The court slapped the man with a 4,000-Swiss-franc (£3,200) conditional fine.