The role is likely to come with equity following the buyout of Clear Channel by the private equity buyers Thomas H Lee and Bain Capital Partners in July last year.
Eccleshare will take charge of all Clear Channels' international poster businesses outside its core US homeland.
Eccleshare joined BBDO as its European chairman in 2005. Before that, he was the European chairman and chief executive at Young & Rubicam.
His departure from Y&R resulted in a High Court action over the length of gardening leave imposed on him by the agency.
Eccleshare spent 18 years at JWT, beginning in 1978, where he progressed to become the network's worldwide director of strategic planning.
He then moved to Ammirati Puris Lintas in 1996 as the chief executive and then chairman.
Eccleshare was unavailable to comment.