UBS, beset by heavy losses and a large tax evasion case in the US, said its chief executive, Marcel Rohner, has resigned and will be immediately replaced by Oswald Grübel, who joins from rival bank and wealth management group Credit Suisse.

Mr Grubel has worked for almost 40 years at Credit Suisse. Between 2003 and 2007, he was chief executive at the Zurich-listed bank.

“With his indisputable leadership qualities, combined with his extensive expertise, Oswald Grübel brings the ideal skill set to recreate value, together with our management team, for our shareholders and clients. He will also be adept in balancing our focus on prudent risk taking and client confidence, and our goal to position UBS for future success,” said Peter Kurer, UBS chairman, in a statement.

UBS has booked almost $50 billion in losses from the credit crunch and last week agreed to pay a $780 million fine to the US authorities over charges that it helped wealthy US citizens evade taxes. It is still embroiled in a legal fight over demands from the US tax authorities to hand over data on 52,000 US clients.

Mr Rohner had told the UBS board in January this year that he wished to step down, Mr Kurer said.

Explaining his move to UBS, Mr Grubel said: “I am convinced that the Swiss financial centre requires the presence of more than one big global bank. The opportunity to lead UBS with its unique client franchise in wealth management, investment banking and asset management in these extraordinary times presents a fascinating, yet formidable challenge to me. Together with our 77,000 dedicated employees, I will do all I can to bring UBS back on a profitable, successful track.”