As previously reported by CNET News.com, Cast, 41, succeeds John Fleming, who was promoted to chief marketing officer for parent company Wal-Mart in April.
Effective July 5, Cast will be responsible for the day-to-day operations at the retailer's Web site and will report directly to Fleming, the company said.
Cast joined Walmart.com in 2000 as vice president of marketing and later left to join eBay. He worked at the online auction company for four months before resigning earlier this week.