Cornwell's signing marks his return to the industry after quitting his role at Tequila\ in March 2005, soon after its merger with the fellow Omnicom-owned agency TBWA\GGT, where he had held the position of chief executive.
Before joining Soup, Cornwell had considered launching a start-up, with The Red Brick Road as one of a number of potential backers. He starts in his new role next week, where he will join the founding partners, Nick Thompson, Shaun Freeman and Simon Coupe, who set up Soup ten years ago.
Cornwell will not receive equity in Soup, which has offices in London and Norwich and has produced digital work for clients that include Fuji Film, Royal Bank of Scotland, Virgin and Norwich Union.
Cornwell said: "I see joining a digital agency that is up there with the very best as the perfect re-entry point to the industry."