Craze comes to the chairmanship at a crucial time for the body. Earlier this month JCDecaux, one of the OMC’s four council members, pulled out of the OMC.
The outdoor industry has commissioned Craze to conduct a review of OMC's business in October 2014, to look at the "role, activity and direction" of the organisation.
Craze presented his report to the OMC board in late 2014, but his appointment and the review were considered independently, Campaign understands.
It is the first time the body's chair has not been an executive within the industry. Patel is the chief executive of Primesight.
He said: "Our media sector is poised to take a great step forwards. When I was appointed chairman I realised that we needed to reinvigorate the OMC and Mark's experience will be invaluable in helping demonstrate the potential to advertisers, brands and media and creative agencies.
"He has the gravitas, the clout and the contacts to really help raise the OMC to another level."
Craze left his role as the group chief executive of Havas Media UK in February 2014. He joined Havas Media as managing partner in 2005 and was promoted to group chief executive in 2008.
Prior to Havas, Craze was at Aegis Media UK for 15 years, latterly as the chief executive from 2002 to 2004.
Craze said: "The out of home industry is at the most exciting point in its history, and I have been massively impressed with the commitment and energy of all the contractors supporting the OMC.
"On the back of huge investment, new technology and improved audience insights, out of home (OOH) has enjoyed spectacular success over the last ten years, and is now passing the billion pound mark in ad revenue.
"Our ambition is to unleash the full innovative potential of OOH and work even more harmoniously with advertisers, agencies and the Specialists.
"Our single minded goal is to further drive growth and enhance our position as the most innovative, engaging and influential form of advertising."
The OMC's chief executive, Mike Baker, announced his intention to step down in October and expects to complete work in March. He rebranded the group as OMC and ushered the group through a new marketing-led approach.