Cowie's brief will be to develop new-business opportunities for the agency with existing and new clients. He reports directly to the chief executive, Simon Bolton.
The news follows the departure of the previous marketing director, Claire Durward, by mutual consent in February after only ten months in the role.
Her replacement, the agency's marketing director, Kate Bruges, will report to Cowie.
Cowie has spent the past year developing Flipem, a digital service allowing people to send a bet as a gift.
Before that he had been at AMV and before that was the marketing director of Sharepeople.com. He joined Brunswick PR in October 1997 to develop its advertising and corporate marketing, and before that spent three years as the head of sales and marketing at Two Way TV.
Cowie began his career at Ogilvy & Mather and has also worked as the client services director at WCRS, and as a board account director at Collett Dickenson Pearce.
Bolton said: "I've seen a number of candidates for this position, but Peter stands head and shoulders above the rest because of his unique blend of commercial and creative experience."