Sir Nicholas Macpherson, the permanent secretary to the Treasury, is stepping down after 10 years in the role.
Macpherson, who has worked alongside three chancellors in that position, will step down on 31 March, the Treasury confirmed today.
He was appointed permanent secretary in August 2005, following the departure of Sir Gus O’Donnell. Before that he held a number of roles in the Treasury, which he joined in 1985.
Macpherson said: "It has been a privilege to lead the Treasury through an extraordinary period. But after 31 years in the department, and having worked on 33 Budgets and 20 Spending Reviews, it is time to do something else while I still can.
"With the fiscal strategy for this Parliament set and the economic recovery well established, now is the right time to stand aside and for someone else to guide the Treasury through the challenges ahead.
"I pay tribute to the remarkable energy, creativity, resilience and decency of the Treasury ministers and officials I have worked with."
George Osborne praised Macpherson as "one of the outstanding public servants of his generation".
"He has been at the helm of the Treasury during the most difficult decade of modern economic policy making and his advice to me has always been intelligent, candid and discreet. He will be sorely missed by the official team he has built up at the Treasury and ministers, like me, lucky enough to have worked with him."
The process for selecting a successor will be announced in due course, the Treasury said. The department hopes to have a replacement in the role by 1 April.