Faster Horses is designed as a "bolt-on" creative department and will offer creative concepts and strategy.
Walker and De Souza have not yet recruited permanent staff but will work with a range of partners, including third-party production, design, digital and experiential companies, to deliver multichannel campaigns when required.
The agency’s first work, a project for Uniqlo shot by Rankin, breaks on TV during the Channel 4 drama Indian Summers on 13 March. It will take up the full two-and-a-half-minute ad slot.
The campaign is to relaunch the retailer’s flagship store at 311 Oxford Street, which Uniqlo wants to function as a cultural hub. The clothing brand has set up partnerships with Tate Modern and East London’s NTS Radio, and will sponsor a series of late-night events at the gallery as well as cultural talks and a summer rooftop barbecue.
Walker and De Souza joined Karmarama as creative directors from Fallon in 2010. The pair were made partners and executive creative directors at the agency in 2013. They were promoted to group executive creative directors in 2014.
The duo’s most high-profile work at Karmarama was "God Only Knows" for BBC Music in 2015. They also worked on Costa and Virgin Active.
The pair left the agency at the end of July last year following the appointment of Nik Studzinski as the chief creative officer.
Walker said: "The ambition for Faster Horses is to be an agile and highly experienced creative resource, not just for brands and agencies but for start-ups and media and PR companies – and anyone looking to make an impact with exceptional creative work."