Martin Lack, a former senior UBS private banker, has pleaded guilty to conspiring to help wealth Americans hide millions of dollars for 17 years in offshore accounts.
Lack admitted in the federal court in Fort Lauderdale, Florida in relation to a criminal indictment in 2011 for helping rich Americans to evade taxes.
Lack was accused on a charge of conspiracy to help US clients in opening and maintaining secret bank accounts at UBS and a Swiss cantonal bank for hiding income and assets and filing false tax returns.
As part of the plea, US prosecutors have proposed Lack be sentenced to five years probation.
However, a formal sentencing for Lack has been scheduled for 7 May.
Lack has admitted to US authorities in October and has returned to Switzerland on $750,000 bail.
In 2009, UBS paid a penalty of $780 million as a settlement and assured to reveal the names of US clients.
William Dimitrouleas, US District Judge, said: "The agreement also recommended that Lack receive no fine or be forced to make restitution. As a condition of probation the lawyers are going to recommend that I require you to cooperate in any investigation they might be interested in."