Hyams' new responsibilities have come after almost three years at the helm of MEC Interaction.
He will be working with local heads of MEC operations as well as those who run individual disciplines across markets in a bid to make the network more integrated.
Varley said: "Jeff has a wealth of experience in traditional media and was one of the pioneers of digital media communications."
Hyams said: "Coming from the digital space, I am aware of how fast things are changing in terms of how we work, and the need for integration."