The biggest US-based clothing retailer did not provide further detail on the reasons for Peck's resignation after serving as CEO since 2015 and working at the Gap for almost 15 years.
The company said, however, that Robert Fisher - a Gap founder and currently the company’s non-executive chairman - will serve as CEO on an interim basis.
Gap's shares plummeted over 9 percent on Thursday on the news of Peck's sudden resignation.