At Ipsos, Green will focus on developing the Ipsos Media approach to ROI, engagement and mobile.
Green was director of strategic insights ZenithOptimedia, and previously held senior positions at OMD and Zenith in the US and Asia.
Richard Silman, CEO of Ipsos Media, said: "I have known and worked with Andrew for over 20 years in a number of capacities, and his knowledge and experience will bring enormous benefits to us and our clients."
Green said: "This is an exciting time to be in media research. All the old assumptions are being challenged and new ways of measuring audiences are being pioneered. Ipsos is ahead of this curve and I look forward to helping them to tell this story around the world."
Ipsos Media is currently established in over 25 countries worldwide and Green will play a key role in its development, especially in the Asia Pacific region.