Wal-Mart Stores Inc. will give nearly all its U.S. hourly store employees—and not just minimum-wage earners—a raise next month, as the nation’s largest private employer tries to combat a tighter labor market and the turnover endemic in the retailing industry.

Wal-Mart previously said it planned to boost its minimum wage in February to $10 an hour. But the giant retailer said Wednesday that hourly workers employed in its stores as of Dec. 31 would get at least a 2% pay bump. The wage increase will affect nearly 1.2 million...