Raoul Weil, 54, had been staying in a luxury hotel in the city of Bologna where he checked in under his real name, triggering a police check because he is on an international fugitive list.
"He was arrested at the hotel and he is now being held in prison. He did not explain why he was in Italy," a spokeswoman for Bologna police said.
The officer said the arrest took place on Friday but explained that details of the case were only being released on Sunday because of police policy.
Weil, who was chairman of the global wealth management service at UBS in Zurich, was indicted by a federal grand jury in 2008 for his alleged role in overseeing the US cross-border business.
The Swiss national always denied the charges and had been declared a fugitive by the US courts.
According to the indictment, between 2002 and 2007, Weil supervised the Swiss bank's overseas activities that serviced some 20,000 customers.
The indictment alleges Weil and co-conspirators helped US customers conceal around €15 billion in assets from tax authorities.