John Tiner, chief executive of the Financial Services Authority (FSA) is stepping down in July in order to work in the private sector.
Tiner, 49, has headed the FSA since September 2003 and is leaving because he wants one last significant job in the private sector before he retires.
He joined the financial regulator in April 2001 as managing director of the consumer, investment and insurance directorate. He was appointed chief executive in 2003.
In a statement Tiner says: "I would like to do another job in the private sector before I think about retirement and this seems to me to be the right time to pass on the baton."
FSA chairman Callum McCarthy says Tiner "has been a leader in developing international regulation through his work in Europe".
McCarthy will lead a committee that will conduct a search among both internal and external candidates for a successor.
FSA managing director Clive Briault is tipped as favourite to take over Tiner's role, followed by managing director Hector Sants.