Agencies with representatives on the council include Chemistry, Stephens Francis Whitson, Meteorite, Rapp, Watson Philips Norman, Carlson, Baber Smith and Mindshare.
Arnold took over as chair from David Poole, founder of DP&A, in 2005 having been chair of the Creative Council for three years.
"We've taken on some big issues and concentrated on long term projects - revising brief guidelines, looking at copyright and intellectual property rights) and other issues," Arnold said.
"Recently we completed a major project, Return on Ideas. It's been a dynamic and hard working council that is making a real difference. But after four years I have decided now was a good time for a change."
, the ethical marketing agency he set up in 2002, late last year to set up to write a book, Ethical Marketing & the New Consumer for publishers Wiley's, and to plan the launch of Creative Orchestra.