Clark was most recently the deputy business editor at The Times and managed a team of 25 journalists across its print, web and tablet editions.
The department was named Business and Finance Team of the Year at the 2011 British Press Awards.
Clark was previously business editor at The Observer and he covered the global financial crisis on behalf of The Guardian as its US business correspondent.
He has also had stints at Euromoney Publications and The Daily Telegraph.
Stephen Day, chief operating officer and managing director of BM's public affairs practice, said: "Understanding the media is a key component of any public affairs strategy and in Andrew we have a heavyweight who can offer senior counsel and strategic advice drawn from his years of experience as an award-winning journalist and observer of international affairs, business and politics."