Martyn takes up the role from August 2, having originally joined the company in 2013 as Marketing Operations Director.
The company said he has played a pivotal role in the management and development of internal marketing operations, and has recently spearheaded the relocation of InterMedia's fulfilment business, InterSend, to a new facility on the Gatwick industrial estate.
Martyn will maintain his current responsibility for the InterSend operation in his new role as well as taking Board responsibility for the recently created Central Operations team.
In a statement, the company congratulated Martyn on his new position, which it said formed part of its continued "pursuit of growth, operational excellence and efficiency across the Group".