"This is a very natural progression," said Brian Sozzi, chief executive and chief equities strategist at Belus Capital Advisors. "Wal-Mart's engine of growth has been international."
McMillon faces challenges. Wal-Mart is seeing its low-income shoppers in the US struggling with stagnant wages and rising costs. At the same time, Wal-Mart faces fierce competition from online competitors and dollar chains. The company also has image problems.
Wal-Mart is being pressured to further increase its oversight of factory conditions abroad following a building collapse in April in Bangladesh that killed around 1127 garment workers. And it continues to face criticism over its treatment of its hourly workers.
Additionally, allegations of bribery in Wal-Mart's Mexico operations that surfaced in April 2012 have slowed business overseas. Wal-Mart allegedly failed to notify law enforcement that company officials authorised millions of dollars in bribes in Mexico to speed up getting building permits and gain other favours.
The New York Times, which broke the story, reported that Wal-Mart officials, including Duke, were allegedly informed starting in 2005 about the bribes. McMillon was not linked to the incident because he wasn't working in the international division at the time.
Dave Tovar, a Wal-Mart spokesman, said that Duke's decision to leave Wal-Mart was "a personal one", and had nothing to do with the bribery allegations.
"He decided it was time to retire," said Tovar, who added that Duke approached Walton and the board voted on Saturday.
Duke became chief executive in February 2009 at a time when the retailer's strong performance made it the rare winner during the recession. But that soon changed a few months after he took the helm.
As the economy slowly recovered, times got tough for Wal-Mart, resulting in a more than two-year slump in its US namesake business.
Duke named a new US executive team, which reversed the slump in the third quarter of 2011 by restocking thousands of items that had been ditched and pushing low prices across the store.
But those gains have been reversed since early this year. Wal-Mart lowered its profit outlook twice in three months.
Duke will remain as chairman of the executive committee of the board. In the tradition of his predecessors, he will stay on as an adviser to McMillon for one year.
Meanwhile, the company said it plans to name McMillon's successor by the end of its fiscal year in early 2014.
- AP