Lindsay's resignation leaves Publicis without a chairman, chief executive or managing director. He is expected to remain at Publicis until the network's chief operating officer, Richard Pinder, tracks down a successor.
Lindsay and Pinder announced the resignation to the agency's 550 staff on Wednesday afternoon.
Pinder told Campaign: "Tim and I have been discussing his role since the difficult news over the turn of the year. Publicis UK is now over this tough time, and is recording new wins and new growth with the formation of Publicis Modem, but Tim's heart was not in it; he wanted to leave, despite having our full support.
"I know he will be with his team until his successor is announced. I am exploring all the right avenues for this important decision."
One option understood to be under consideration at a Publicis Groupe level is the merger of Fallon into Publicis.
Fallon shares the Cadbury account with Publicis, and also handles the Asda brief. A merger would give Publicis access to Fallon's strong management team.
Publicis, the UK's fifth-biggest agency, has lost several key accounts over the past six months; Asda, MFI, the Post Office and Cadbury have all moved their business elsewhere. In March, its chief executive, Grant Duncan, resigned in the aftermath of the account losses.
Lindsay joined Publicis in March 2004. Since then, he has worked hard to promote the agency's integrated offer, restructuring Dialog and the advertising agency to work more closely together.
- Perspective, page 19.