Organic, Swirl and Digitas were the finalists in the pitch, which lasted several rounds, the source said.
Digitas will run the account from its Chicago office, the source added.
Advertising Age, which first reported the story, the digital-media budget is between $20 million and $30 million.
Ebay’s sales and marketing budget was $2.4 billion in 2011. According to a Kantar Media report, eBay reduced its Internet advertising budget, which included display and paid search, by 2.0% to $173.2 million in 2011.