Shepherd will be based at GMI's EMEA regional headquarters in London and has been tasked with handling existing customers and bringing in new clients.
He has joined the company after a spell as director of sales at research company Holden Pearmain.
He began his career at Mintel, where he spent nine years working across a range of markets including FMCG, retail, leisure and media; he also managed a sales team that was responsible for a multimillion-pound turnover.
Dietmar Walker, EMEA executive vice-president of GMI, said: "Matt has extensive experience in the market research industry, and his ability to form strong relationships with senior-level executives will be vital as we continue our growth."