The decision will mean the creation of a larger media network with combined operations in Beirut, Riyadh, Casablanca and headquarters in Dubai. Media Insights is partially owned by Grey Global.
The agencies will handle clients including Nestle, National Bank of Abu Dhabi, Volkswagen Audi Group, P&G, Shell, Aujan and Turkish Airlines.
Eric Hanna, formerly Grey Group's Middle East and North Africa (Mena) chief operating officer, will now lead the MediaCom Mena network from Dubai, reporting directly to Nick Lawson, the MediaCom EMEA CEO.
Hanna said: "Leading MediaCom and supporting the seamless merging of two WPP agencies in the region is a challenge, one I am really excited to take on.
"The two teams are a solid match in terms of skill set and outlook. Everyone in the region is ready to leverage the power of MediaCom globally to offer clients differentiating media solutions that help build their brands and as a result, business."
Lawson said: "The Mena region has shown real resilience over the past year or two making it strategically important for our global operation and a focus for further investment. It was imperative that we identified the right person for the job and in Eric Hanna, we believe we have.
"Eric has very solid knowledge of the region having worked there for many years. This combined with his experience both in house and agency made him the ideal candidate to lead MediaCom into this new phase of its life."