New York Federal Reserve Bank President William Dudley, a key figure in the unprecedented government response to the financial crisis, will retire in mid-2018.

Dudley, who has headed the bank since 2009, will likely retire sometime in the spring or summer of 2018 when his replacement is found and approved, sources told CNBC. His term ends in January 2019. A search committee has already been formed.

The New York Fed confirmed the plans Monday morning.

Dudley, who will be 65 next year, took the helm of the New York Fed when the banking system was still in the throes of the worst financial crisis of the post-war era.

He previously had headed the New York Fed's markets group, a critical job that oversees the trades and market operations required to set the Federal Funds Rate. In both positions, Dudley was a principal player in Fed decisions concerning the demise of Lehman Brothers, AIG and Bear Stearns, along with emergency measures taken by the central bank to stanch a meltdown in the financial system.

Largely under Dudley, the New York Fed was responsible for accumulating the trillions in assets the Fed purchased as part of the quantitative easing program, bringing its balance sheet up to $4.5 trillion. It is now responsible for the market operations underway to reduce the balance sheet.

Dudley had told several colleagues he was planning to leave in 2018, and his departure is said to not be related to the decision last week by President Donald Trump to name Fed Governor Jerome Powell as the next Fed chairman. In doing so, Trump declined to renominate current Chair Janet Yellen, with whom Dudley has worked closely over the past several years.

Dudley's departure comes at a time of dramatic change at the Fed. In addition to a new Fed chairman, Vice Chairman Stan Fischer left his post in October, and there are currently three open seats on the seven-member Board of Governors. That number may rise to four if Yellen leaves the board when Powell is confirmed and before others are nominated and confirmed by the Senate.

As president of the New York Fed, Dudley holds a special spot among the dozen regional bank presidents. The incumbent always serves as vice chairman of the rate-setting Federal Open Market Committee and always votes at policy meetings; other regional presidents have a rotating vote.

The choice of Dudley's replacement will be made by the New York Fed's board of directors and approved by the Federal Reserve board.

"I would especially thank Tim Geithner, Ben Bernanke and Janet Yellen for giving me the opportunity to work closely with them during the crisis and the subsequent economic recovery," Dudley said, in a Monday morning statement. "I am extremely proud of the work we have done in New York, and as a System, from our efforts to help the nation navigate the financial crisis to beginning the process of normalizing the balance sheet to our work on reforming the culture of the financial services industry."

Prior to joining the New York Fed, Dudley served Goldman Sachs as chief U.S. economist and a managing director.