The role is newly-created and Rosen will report to James Hilton, global chief executive of M&C Saatchi Mobile.
Rosen, who left O2 owner Telefonica in the middle of last year, has been consulting with M&C Saatchi Mobile for the past six months before deciding to join in a more permanent capacity.
"It's a successful company that has grown quickly. But they haven't really built up a global function that allows them and their clients to take advantage of their 10 offices around the world," Rosen explained.
His role, therefore, is to help put processes in place that ensures the network is using its global reach and capabilities for clients.
"This includes anything - from enabling the chief executive’s vision to creating, shaping and adapting the necessary infrastructure, products, clear processes," Rosen said.
Another of his key focuses will be building out the agency's global data capabilities. "Data is already at the heart of how we produce our best work for clients, but I'm here to make sure we're honing all the learnings we have gained in one region and applying it across the network," he said.
Other key areas of growth for the mobile-first digital agency, Rosen observed, lie in understanding the dynamics of app stores and strengthening client work in terms of rich engagement on mobile.
Rosen joined Telefonica in September 2014 from WPP agency Joule where he was global chief executive. Prior to that, he founded and led AKQA's mobile practice for eight years.