Darwell-Taylor joins after a spell as a freelance creative director on both the client and agency sides.
Most recently, he worked at Barrett Cernis, after a stint at BSkyB. His career includes spells at Joshua, Mother and Rapier, and working in-house for Red Bull.
He is best known for founding the Body Shop's in-house creative department, The Creative Greenhouse, with Anita Roddick. He has also written and directed a short film called Out of Depth.
Darwell Taylor replaces Jack Nolan and Graham Mills, who left the agency unexpectedly in October for personal reasons. In the interim, the department has been overseen by the deputy creative directors Garry Munns and Aaron Martin.
Mike Spicer, the managing director of Arc London, said: "Replacing Graham and Jack was never going to be easy, and we took our time in order to find someone who could not only build on Arc's creative reputation but inject some enthusiasm. What attracted us to Simon was his ability to see beyond 'the line' and create big ideas to work across any media."