Gary Cohn, of Goldman Sachs, said financial firms ?want to stay in London? ? and Britain staying in the EU was the ?best thing for all of us.?
Some firms fear EU states could impose costs on UK-based banks to operate in the EU if Britain left the union.
But some business figures have called for Britain to pull out.
Mr Cohn said: ?I think for the UK it?s imperative to keep the financial services industry in London.
?We all want to stay in London ? it is our European headquarters.
?I think that having a great financial capital of the world staying in the UK and having the UK be part Europe is the best thing for all of us.?
BBC business editor Kamal Ahmed said the prospect of a referendum on Britain?s EU membership if the Conservatives win May?s general election had ?raised fears that withdrawal could lead to many foreign banks moving their headquarters out of the UK?.
He said this could be caused by the EU?s use of ?passporting rules? which could mean banks had to move their headquarters to EU countries or face higher costs.
Passporting allows financial firms to conduct business in any state within the European Economic Area under a series of single market directives ? a right UK companies could lose if Britain exited.
Business leaders including the Confederation of British Industry and Virgin boss Sir Richard Branson have said Britain should stay in the EU.
But inventor Sir James Dyson said in November that he would vote to leave the EU to avoid being ?dominated and bullied by the Germans? ? though he said he wanted to keep free trade and free movement of people.
Businessman Paul Sykes, one of Britain?s richest men, is a major financial backer of the UK Independence Party and has criticised the UK?s main political parties for their ?slavish support for the EU?.