Martell will report to Richard Morris, Vizeum’s managing director.
Joining MediaCom in 2002, Martell became a global strategy director last year. She worked on Mars, Universal Pictures, Sky, Now TV, Boots, eBay and Sony.
Between 2001 and 2002, Martell was a communications planner at St Luke’s. Before that, she spent a year in Australia at OMD.
Jem Lloyd-Williams, the executive director for product and innovation at Vizeum, said: "Lou offers fantastic strategic thinking, a natural flare for honing and simpli-fying ideas and a forensic knowledge of how best to activate in all channels."