In the short term, WCRS said it would not be seeking a replacement. The chief executive, Stephen Woodford, denied there was any element of cost cutting involved in the move and said the agency aimed to introduce a "flatter" management structure.
The department heads that reported to Coward - which include the head of planning, Debbie Klein, the creative director, Leon Jaume, the head of television, Sarah Bales, and the head of account management, Emma Lawson - will now report directly to Woodford.
A total of 12 staff, from a previous five, will now liaise directly with Woodford.
"The current management structure will remain in place. In a sense all we are doing is taking one layer of management away," Woodford said. "WCRS's department heads work with a lot of autonomy so it won't be a large new burden for me and they will take on more responsibility themselves. If you look at other agencies our management structure is about average, not light, but certainly not top heavy."
Coward's departure comes weeks after WCRS failed to win the £43 million Orange account. Coward ran the pitch in conjunction with WCRS's chairman, Robin Wight.
But Woodford stressed the move was in no way linked to the agency's failure to recapture the Orange account, which WCRS launched in the UK. "Had we won Orange there may have been a different outcome but this is not connected with the Orange pitch. It would have been a big new client for us but the two events are not linked."
Coward worked on the Orange account before it moved to Lowe Lintas two years ago. He subsequently managed the agency's Vodafone business, until it moved to J. Walter Thompson earlier this year.
Coward joined WCRS as a group account director from TBWA GGT Simons Palmer in 1998 and took on the role of managing director in March last year.
He has also worked on accounts including Sky, Sega, Sara Lee and Danish Bacon.