Tim Lindsay, the UK group chairman of Publicis, is to take on Grant Duncan's duties at the flagship London agency, following the resignation of the chief executive.
The agency, which is making a number of redundancies, is under extreme financial pressure following a number of recent account losses, including MFI (£27 million), Asda (£43 million) and the Post Office (£12 million).
Publicis claims that Duncan had already been considering resigning from the agency in order to pursue outside interests, and that he had decided his departure would alleviate the financial burden.
News of his resignation broke on Tuesday, when Campaign revealed the story on the Brand Republic website.
Lindsay refutes the claim that Duncan was forced out of the position. He said: "He's been a real gent. He's been incredibly loyal and a great partner for the past three years. He's put the wellbeing of the agency before his own.
"There are still a few of us left on the senior management board who can take on the responsibilities. There is already a plan and a talented group of people in place."
Since joining the agency as the managing director from the TBWA Group in 1999 (he was promoted to the role of chief executive in 2003), Duncan has helped steer Publicis through a stable, if unremarkable, period. The business has grown to become the fifth-largest UK agency by billings.
However, the recent problems have upset the stability of the agency.
Duncan said: "The problems happened on my watch, so I do have to take some responsibility. But I'm still leaving a stable agency that has a huge list of big clients and that has achieved great organic growth.
"The agency often gets criticised for not being dynamic enough, but stability is a great business plan. And we still create great work."
Lindsay added: "It's fair to say that we have experienced a blip, but I think it's unfair to say we are troubled. There is no great malaise at the agency. In a few weeks, when everything has calmed down and we're through this, we'll still be profitable and creating good work."