As a creative director, he will work with the agency's founding partners Duncan Bird and Natasha Jakubowski on clients including Coca-Cola, the Association of American Advertisers and Sony BMG.
Andy Amadeo, a former executive creative director of Mustoes and CDP, who has been freelancing at Dare for the past few months, will take Cooper's position as co-head of Dare's creative department.
Cooper has been at Dare since 2005, working alongside the creative partner Flo Heiss across clients including ITV, Sony and Vodafone Europe.
Before that, he worked at Agency Republic as the creative director on O2, the BBC and Smirnoff.
Bird said: "First hires are critical to the development of any new company and James' skillset is perfect for the opportunities we are creating."
Amadeo, who left Mustoes in 2005, has since freelanced at agencies including Fallon Minneapolis, Wieden & Kennedy Amsterdam and Publicis Mojo, New Zealand.
Between 1997 and 2001, Amadeo worked at Lowe Howard-Spink, where he created the Stella Artois "bottle" print campaign that scooped a Grand Prix at Cannes.