Di Piazza, who retired from PricewaterhouseCoopers in 2009, will be a vice chairman in Citigroup's institutional clients group and a member of the bank's senior strategic advisory group.
He will help Citigroup win more business from international institutional clients, Chief Operating Officer and investment bank head John Havens said in a press release.
Di Piazza is the latest in a string of veteran bankers and government figures that Citigroup has hired over the past year, as the third-largest U.S. bank slowly recovers from the financial crisis. The bank lost business, talent, and its reputation after taking $45 billion in U.S. government bailouts over 2008 and 2009.
Since then, Chief Executive Vikram Pandit has returned the bank to profitability and has started to rebuild the ranks of its senior executives. One of his most prominent hires was Peter Orszag, U.S. President Obama's former budget director, who joined the bank as a senior adviser late last year.
The bank's hiring spree has continued, especially as Citigroup tries to recover lost ground in its investment banking business. For example, Citigroup hired Doug Baird, a top equity capital markets banker from rival Bank of America Corp
(Reporting by Maria Aspan, editing by Dave Zimmerman)