The appointment comes 12 months after the agency hired Fiona Battle in a similar role. According to Battle's LinkedIn profile she left the agency in December.
Cox, who has joined as head of Mediaco UK and EMEA, will be responsible for driving business development, strategy and client innovation through the integration of digital and content publishing.
He will be based in London with an EMEA-wide remit, reporting to Mediaco global head Jason Wellcome.
Cox comes from marketing and technology agency DigitasLBi, where he was digital strategy partner and strategic guild leader, and previously worked in digital journalism at BBC News and the Australian Associated Press.