Reid joins the company from McKinsey & Company, where he was a senior manager of its European media and telecoms practice.
His new role at Media Square will entail coordinating business pitches and working with individual business units to look at ways of improving operating margins.
At McKinsey, Reid managed teams behind a number of projects, including developing a growth strategy for a leading global media brand.
He began his career at international management consultancy Sibson Consulting and has an MBA from Insead in France and Singapore.
Earlier this year, Media Square appointed Roger Parry as executive chairman, a move that drew criticism from Kelvin MacKenzie, the former editor of The Sun, former non-executive of Media Square and a shareholder of about 1% of the marketing services business.
MacKenzie wrote a letter demanding that Parry step down, resign his other business positions or appoint a full-time chief executive. Parry responded by saying that a number of his other roles were non-executive roles and accused MacKenzie of seeking publicity with his comments.
Parry was parachuted into Media Square in June, replacing chief executive Jeremy Middleton, as the group reported a £3.2m annual loss.