Mr Sants joined the FSA in 2004 as managing director of wholesale and institutional markets before becoming chief executive in July 2007.
He initially intended to leave the regulator in the summer of 2010 but was asked to stay to implement the new tri-partite regulatory structure of the Financial Conduct Authority (FCA), Prudential Regulatory Authority (PRA) and the Financial Policy Committee (FPC).
He was then appointed chief executive designate of the PRA and a member of the FPC at the Bank of England.
Mr Sants said: “When I agreed to stay on as CEO in 2010, I committed to stay and deliver an orderly transition to the Government’s new regulatory structure.
“The project is now firmly on track and with the establishment of twin peaks within the FSA I will have achieved that goal.”
Lord Turner, FSA chairman, said: “I am very sorry to see him leave but I understand his decision, now that he has delivered what he set out to achieve. I’d like to thank him for all that he’s done.”
The twin peaks model, intended to replicate the split of the PRA and the FCA, will be implemented in April.
Mr Sants is the second senior FSA staff member to leave the regulator. Margaret Cole, managing director of the conduct business unit announced earlier this year she would be leaving at the end of March.
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