Eccleshare is currently chairman and chief executive of Y&R/Wunderman for the EMEA region, a position he took up in 2002 after a two-year absence from the ad industry, when he worked as a consultant for management consultant McKinsey.
His start date at BBDO is not yet known, but he will report to worldwide chief executive Andrew Robertson and will take the role of chairman and CEO of EMEA. The post also includes responsibility for BBDO's direct marketing network Proximity.
In the new role, Eccleshare will be looking at building the relationships between BBDO's local advertising agencies, which include Abbott Mead Vickers BBDO in London and BBDO Paris.
He takes over from Jean-Michel Goudard, who is to retire at the end of the year.
Robertson said: "As many of you know, Jean-Michel Goudard has been threatening to retire for more than two years now, and made it clear to Allen [Rosenshine, chairman] and I that 2005 will be his last full year.
"He has spent the last few years focused on Europe, Asia, and, within that, Japan in particular. In discussing the future with him and Allen we have agreed that, given the scale, scope, complexity, and potential, of our European businesses, BBDO EMEA demands 100% focused leadership and management. William is the man to do it."
The move is a blow for Y&R, which is suffering the loss of a number of significant accounts, including Burger King, Computer Associates, Jaguar and Sony Electronics. The turmoil has fuelled rumours that the networks CEO Ann Fudge is on the way out, and the company is already hunting for a new chief executive of the Y&R Advertising division.
Eccleshare, 49, 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 chief executive and then chairman. He was among the senior redundancies made at APL after its merger with Lowe Howard-Spink in 1999, which saw Lowe's Paul Hammersley become chief executive.
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