Asda has moved the business directly from the incumbent, Sales Activation Solutions, which had held the business for more than two years.
Redbus, which already handles trolley advertising for Sainsbury’s and Tesco, will manage sales, marketing and fulfilment for Asda on a long-term contract.
Redbus said the new appointment will help the company reach up to 200 million shoppers every four weeks.
Alan Valler, group sales director at Redbus, said: "Demand from advertisers for in-store media at the points of choice and purchase has grown exponentially, because it is now fully appreciated as one of the most accountable forms of media available.
"Our grocery network allows advertisers to target shoppers with uniform, aggregated, cost- effective and measurable in-store messages, and is a compelling proposition for brands and their agencies."
Sarah Brook, head of Asda media centre, said: "We want to further develop this media as an excellent way of bringing key brand messages into our stores that truly benefit customers, advertisers and Asda alike."