The Polish-born pianist, who has lived in Switzerland for years, made an extraordinary speech before his encores at the Lucerne Festival on Tuesday.
After a short reminiscence of his friendship with Leonard Bernstein, he digressed into a diatribe against the arms industry, singling out the Swiss for criticism over their record of supplying arms to countries that are engaged in civil war.
The audience, which included senior Swiss politicians, responded with tepid applause.
Zimerman last used a concert platform for political purposes in 2009 when he spoke out in Los Angeles against US missile deployment policy. He has not returned since to the US.
The Lucerne Festival said this was the first time its stage has been used for a political speech.