"He did a show last night as part of Bobby Farrell's Boney M and they found him this morning dead in his hotel room," agent John Seine told Reuters by telephone from the Netherlands. Farrell was 61.
"He did not feel well last night, and was having problems with his breathing, but he did the show anyway," he added.
The cause of his death was not immediately clear, said Sergei Kapitanov, representative of St. Petersburg's branch of Russia's investigative committee.
Farrell was famous for dancing and lip synching for the disco band that rose to prominence in Europe, the United States and the Soviet Union with songs like "Ma Baker," "Rivers of Babylon" and "Rasputin."
Boney M was put together by German singer-songwriter Frank Farian who also produced most of the vocals for the group, which stormed to the top of the charts in the late 1970s with a string of disco hits.