The 59-year-old, who bought iconic Italian hatmaker Borsalino and owns energy and gas companies in Asia, was arrested following a request from Italy, a police spokesman in the Swiss city told AFP.
"We did this job for Italy," he said, refusing to provide further details.
Regional Swiss newspaper Corriere del Ticino also reported the arrest. Italy's Ansa news agency quoted sources as saying that Rome had launched extradition proceedings.
Marenco was on the run abroad after his network of Italian and foreign companies got involved in a €3 billion crash, according to Italian media reports.
Marenco had bought Borsalino, which was set up in 1857, to diversify his portfolio. The company has served an A-list clientele from former Japanese emperor Hirohito to Hollywood greats like Humphrey Bogart, Warren Beatty and Gary Cooper.
The company, whose fedoras and Panama hats are sold in upmarket outlets, even has movie credits including the 1970 gangster classic 'Borsalino' starring two of France's biggest stars - Alain Delon and Jean-Paul Belmondo.