Wegelin, based in the small Swiss town of St Gallen, started in business 35 years before the US declaration of independence.
It becomes the first foreign bank to plead guilty to tax evasion charges in the US.
The Wegelin case comes four years after Swiss bank UBS agreed to pay a $780m in fines under deferred prosecution agreement. A deferred prosecution agreement is when a fine is paid in exchange for the charges being dropped.
It remains to be seen whether US authorities will continue with, or drop, parallel charges against three Wegelin bankers, Michael Berlinka, Urs Frei and Roger Keller.
