Lecosse will leave the Havas-owned network in six months, until this time he will focus on acquisitions in the Asia-Pacific region. He has been in the top job at the European network for the last 11 years.
The outgoing chairman and CEO will not be replaced; instead a new European management team will be installed with immediate effect.
David Jones, global chief executive of Worldwide, said that four of the network's regional CEOs will add co-managing director duties to their current responsibilities.
The regional CEOs are: Gilles Berouard, CEO of Euro RSCG Northern and Eastern Europe; Andreas Geyr, CEO of the Euro RSCG Germany group; Juan Rocamora, CEO of Euro RSCG Southern Europe; and Christian de la Villehuchet, CEO of Euro RSCG Benelux.
Jones said: "Juan, Gilles, Andreas and Christian will focus on driving growth, accelerating the roll-out of our digitally integrated model and continuing to attract some of the world's best creative talent.
"We at Euro have a fundamental belief that teams make better leaders than the lone individual; it's how we run all of our key divisions, how we run Havas and how we have delivered last year's record results at Euro RSCG Worldwide. This new line-up reflects that philosophy."
The new team is responsible for driving revenue growth, improving the network's creative product and its digital offering.
The appointments do not affect France and the UK, which will continue to report directly to the Euro RSCG Worldwide management team.