Jamie Forese, President of Citigroup Inc. and head of the institutional clients group, speaks at the Milken Institute Asia Summit in Singapore, on Friday, Sept. 19, 2014. Chief executive officers, senior government officials and leading figures in the global capital markets convened at the global conference's inaugural summit in Asia.

Citigroup President Jamie Forese will retire after more than three decades at the bank, according to an internal memo seen by CNBC on Thursday and confirmed by a Citi official.

Forese, who had been considered a possible successor to CEO Michael Corbat, is one of the longest serving executives at Citi. He also served as head of the bank's Institutional Clients Group, which brought in about half of Citi's revenue last year. There, he will be succeeded by his deputy, Paco Ybarra.

"Jamie has played a critical role in cultivating a client-centric mindset across the firm and driving tangible changes to make it easier for our clients to do business with us," Corbat said in the memo. "While I am pleased Jamie will always be an advisor to us, his daily leadership and counsel will be missed by all of us."

Forese's departure is the latest change atop Citigroup, the third largest U.S. lender by assets. In September, the bank merged two Wall Street units overseen by Forese, its corporate and investment bank and its capital markets origination business. That overhaul came days after the firm said longtime Chief Financial Officer John Gerspach and a pair of regional heads were leaving the company.

"Our leadership team has undergone a good deal of change over the last year," Corbat said in the memo. "While we will miss the experience and counsel of those who have moved on, I believe that change is healthy and creates new opportunities for our firm and our people."

The memo did not indicate when the transition would take place.