Miriam Gonzalez Durantez, a highly-regarded lawyer and wife of former deputy prime minister Nick Clegg, is joining the Swiss bank giant's London unit as a non-executive director.
Gonzalez Durantez, who is a partner at City law firm Dechert, will chair the bank's UK audit committee.
A Spanish citizen who herself was unable to vote in June's referendum, Gonzalez Durantez is a specialist in international and EU trade law and her profile on her law firm's website notes she has already been advising her clients on what Brexit means for them.
In the run-up to the referendum, Gonzalez Durantez slammed then-Prime Minister David Cameron's renegotiation efforts with the EU as "Mickey Mouse" and warned that, without urgent growth reform, the country was effectively "sleep walking towards disaster".
UBS declined to comment further on Gonzalez Durantez's appointment.