Magnacca, 50, will also join the board of directors. He was in charge of daily living products and solutions for Walgreen and is the former president of the New York-based Duane Reade chain. Walgreen bought Duane Reade in 2010.
James Gooch stepped down as RadioShack's CEO in September after only a year and a half on the job. The company's profits have fallen over the past two years as brick-and-mortar consumer electronics stores struggle against fierce online competition.
RadioShack shares rose 9 cents, or 2.9 percent, to $3.20 in after-hours trading.