The two groups currently operate either directly or through an affiliation in some countries in the region.
The move will see the their operations grouped into Euro RSCG and Havas Media, with a new focus on markets in Egypt and the Sultanate of Oman, Syria, Kingdom of Jordan, Yemen, Iran, Iraq and the Palestinian Territory.
Havas clients in the Middle East already include Peugeot, Reckitt Benkiser, Danone, Air France, Jaguar and Sanofi Aventis. Chalhoub Group specialises in luxury brands in fashion, gifts and beauty.
Havas-owned agencies, Media Contacts, and Euro RSCG 4D, will also launch in the region in the coming months.
Fernando Rodes, CEO of Havas said: "This deal gives us an immensely strong offer in this key region and is a key part of our growth plans. The Chalhoub Group is the perfect business partner to take on this complex but promising region."