Mr. Duke, 58, is only a year younger than Mr. Scott, 59. The company simultaneously promoted Eduardo Castro-Wright, 53, to vice chairman, adding responsibility for global procurement to his existing duties as CEO of Wal-Mart U.S.
"This management change occurs at a time of strength and momentum for Wal-Mart," said Wal-Mart Chairman Rob Walton in a statement. "Our overall management team has never been stronger."
Mr. Duke had headed Wal-Mart's U.S. operations in the role currently held by Mr. Castro-Wright before taking over the global role three years ago. He became the clear No. 2 executive at the company when John Menzer, 56, retired from his position as vice chairman and chief operating officer earlier this year.
The move allows Mr. Scott -- whose departure became the subject of widespread speculation two years ago amid disappointing results for the retailer -- to go out on a high note. As the economy slips ever faster, Wal-Mart has posted some of the best top and bottom-line results of any retailer in recent quarters.
Mr. Castro-Wright has gotten much of the credit for a turnaround of the U.S. operations, which have posted better same-store sales results than in the past several years, as more shoppers headed to big-box stores in search of bargains and the company focused on improving existing stores as it slowed construction of new ones.
Mr. Duke presided over exiting money-losing operations in Germany and South Korea and increasing focus on more promising markets in China, Canada and Latin America, as well as beginning efforts to expand into India.
"Mike Duke is a highly-respected executive both domestically and internationally, with broad experience throughout the company," Mr. Walton said. He added that "Mr. Castro-Wright has a history of delivering results for our company."
Mr. Duke is only the fourth CEO in Wal-Mart's history, following founder Sam Walton, the 12-year reign of David Glass from 1988 to 2000, and the nearly nine years of Mr. Scott's tenure. Even if Mr. Duke stays until the age of 65, his tenure in the post is likely to be shorter than any of his predecessors.