(Adds details of succession plans, market context)
By Paula Laier and Guillermo Parra-Bernal
SAO PAULO, Jan 20 (Reuters) - Brazil's largest diversified retailer GPA SA tapped a senior executive in Argentina and the former head of Wal Mart Stores Inc's Brazil business to run its struggling supermarket and convenience store unit, according to a securities filing on Wednesday.
Luis Moreno, a Spanish-born executive who ran Libertad, the Argentine subsidiary of French group Casino SA, since 2014, as the unit's chief executive officer. Casino is GPA's controlling shareholder.
The filing said Wal Mart's former Brazil president Marcos Samaha was named as chief operating officer of the supermarket unit, Multivarejo.
GPA CEO Ronaldo Iabrudi would remain in charge until the company found a substitute, probably next year. After that, Iabrudi is expected to become chairman of GPA's board, according to a source familiar with the company's plans.
The company declined to comment on future plans for management.
Brazilian retailers have struggled to keep supermarket sales up in the middle of the worst recession in decades, as rising unemployment and double-digit inflation hit consumer confidence. Net revenue in GPA's Multivarejo unit slipped 0.3 percent in the fourth quarter from a year earlier.
Shares wiped out earlier losses and closed 0.6 percent higher on Wednesday at 35.22 reais. (Writing and additional reporting by Brad Haynes; Editing by Chris Reese and Grant McCool)