Nunwood has brought Walker in as it plots expansion into Europe, Asia-Pacific and the West Coast of the US. It currently has offices in London, Leeds and New York, employs 110 people and has clients including Vodafone, Tesco and Coca-Cola.
Clare Bruce, Nunwood chief executive, described hiring Walker as a "major coup" and said he would play a leading role in the "ongoing transformation of Nunwood's consultative approach, client services and international strategy".
Walker took over Accenture's international Marketing Sciences division, following the acquisition of his business Edge Consulting in 2002.
He grew the practice to more than 20 offices globally, and a team of over 400 consultants, involving the acquisition of the media consultancy Media Audits.
At Accenture he worked with the management teams from many of the world's leading brands including Vodafone, Staples, Dell, and Nokia.
Before setting up Edge he held global leadership roles at MindShare, J Walter Thompson and was chairman of Brand Science.