Brendan McDonagh, the veteran HSBC banker who has been credited with turning around the global giant's money-losing U.S. operation and largely stemming its losses from subprime mortgages, is retiring after 30 years with the bank, HSBC said Tuesday.

In a surprise announcement, the London-based bank said McDonagh, 51, would retire as CEO of HSBC North America Holdings as of July 31. The bank did not give a reason, nor did it say what he would do. Prior to running the North American operation, McDonagh was the bank's top executive in Buffalo for four years.

He will be succeeded by Niall Booker, a 31-year veteran of the bank, who is being promoted from deputy CEO of the North American operation and CEO of HSBC Finance Corp. Booker, also 51, will also become a group managing director, like McDonagh was, and will join the Group management board as of Aug. 1.

McDonagh is widely regarded for his management of the company's U.S. business during the financial crisis. HSBC is one of the few giant banks worldwide that did not require a bailout or other financial assistance from any government, and did not report a net loss for any quarter, despite billions of dollars in bad debts and writeoffs.

"I would like to thank Brendan for his significant contributions across many areas in HSBC and wish him all the best for the future," HSBC Group CEO Michael Geoghegan said. McDonagh "has been instrumental in leading our business there through particularly challenging times in addition to the continued growth in our core businesses."

The Financial Times, citing unnamed sources, said McDonagh stepped down because he had concluded he had little or no chance of becoming CEO of HSBC Holdings Plc, the global parent company that operates in 88 countries and territories worldwide.

Geoghegan, who recently relocated to Hong Kong to emphasize the group's renewed focus on Asia and emerging markets, is expected to remain in that role for several years, and the competition to succeed him is likely to be fierce.

However, given his reputation and relatively young age, industry watchers expect McDonagh to be snapped up quickly by another company.

Booker joined HSBC in 1981, and has served in nine countries, including as deputy chairman and CEO of HSBC Middle East and as CEO of HSBC India. He has also held a total of four positions in the United States during his career.

"The combination of Niall's four U.S. postings during his HSBC career to date and his international experience mean that he is Brendan's

obvious successor for the next phase of developing our business in North America," Geoghegan said.