In the UK, Chris Hirst, the European and UK group chief executive, will take on the additional role of chairman for Havas Group UK.
Yannick Bolloré, chairman and chief executive of Havas, will take on the role in France, Alfonso Rodés Vilà, deputy chief executive of Havas and global chief executive of Havas Media Group, will take on the additional role in Spain; and Andrew Benett, chief executive of Havas Worldwide and chief strategy officer of Havas Creative Group, will do the same for North America.
The new roles are effective immediately, and are announced ahead of all of the London Havas offices moving to Kings Cross, under the same roof. The agency has already done this in New York and Paris.
A statement from Havas said the move will "ensure the creation and development of the most effective, innovative and integrated solutions for clients regardless of where the thinking begins".
Paul Frampton, the Havas Media Group UK and Ireland chief executive, will have a dotted line into Hirst.
Hirst said: "I am immensely proud to be taking a brilliant group of businesses into a significant year for Havas in the UK.
"We will be moving into our new village, integrating our skills and offering our clients a truly competitive communications service in one single home.
"I look forward to working with Paul Frampton and all the HMG businesses to offer a truly client-centric experience."