REUTERS/Dylan Martinez
The appointment of Darling, who was Chancellor of the Exchequer from 2007 to 2010, is effective from January 1, the bank said in a statement on Wednesday.
James Gorman, chairman and CEO of Morgan Stanley, said: "He brings strong leadership experience, as well as insight into both the global economy and the global financial system."
Darling is the latest heavy-hitter from the financial crisis to land a job in finance.
On Monday, PIMCO, one of the biggest fund managers on the planet, appointed former Prime Minister Gordon Brown, former Federal Reserve chairman Ben Bernanke and ex-European Central Bank president Jean-Claude Trichet to its new advisory board.
PIMCO said on the day: "The Board members will contribute their insights to the firm on global economic, political, and strategic developments and their relevance for financial markets," the press release said.
Darling joins Morgan Stanley at a time when the bank is going through big changes to its investment banking structure.
The bank announced cuts in its fixed income desk on Tuesday.The US bank is cutting 1,200 staff, including about 470 front-office staff in its fixed income and commodities business