Hardy will play a central role in the search group's growth and expansion plans and will be charged with strengthening the company's sales and marketing operations across 13 international offices.
Hardy said: "It's a tremendously exciting time to be joining bigmouthmedia.
"This is an industry-leading company that operates in a constantly shifting marketplace, and every day brings a fresh set of challenges. That generates the kind of pace and atmosphere it's impossible to avoid getting caught up in."
"After over 13 years client side this is my first role with an agency -- I was convinced to cross the line because of the strengths of the Bigmouthmedia operation and its plans for the future."
Before joining Marks & Spencer and leading Money's successful ecommerce strategy, Hardy served as online retailing and marketing director at Hilton Hotels International. Prior to that he previously occupied senior roles at American Airlines and HSBC.
Steve Leach, Bigmouthmedia Group CEO, said: "We're delighted to be working with David. He brings a wealth of international business experience to the senior management team that I'm confident will deliver real benefits as we continue to drive the group forward."