The five-year contract gives Adshel the management of a network of 800 six-sheets in Somerfield's 332 UK stores. In Scotland, some of these stores trade under the Mace and Kwik Save brands.
The appointment also strengthens Adshel's retail credentials - the company has an existing contract to represent Sainsbury's. With a market share of 4.1 per cent and a turnover of £5 billion, Somerfield is the UK's sixth-biggest supermarket.
The appointment comes as Somerfield is in the process of a multimillion-pound upgrade of its high-street stores. The supermarket is attempting to move upmarket and has introduced three formats to its stores - Market Fresh, Essentials and Progressive.
Patrick Chaundy, the business development director at Adshel, said: "External point-of-sale is very imposing and provides powerful reinforcement of brands at that crucial time when the consumer enters the shop. It has been one of the fastest growth sectors of outdoor advertising for the past few years."
Marcus Leyden, Somerfield's concession manager, added: "With nine out of ten of our stores being situated in high-street or town-centre locations, they provide an excellent opportunity for suppliers and brands to market their products."