At the same time, Tom Dery, the executive chairman of Asia-Pacific, has been appointed as the chairman of the network. Tim Duffy, the UK chief executive of M&C, will now also take on the role of UK chairman.
Bill Muirhead, the M&C founding partner, said Mac-Lennan will be responsible for bringing cohesion, profile and international business to the network.
He will also be responsible for launching new offices and controlling any future acquisitions - although they will be unlikely in 2009.
MacLennan added: "We have a good profile in certain markets, such as London and Australia, but as a network it's not really talked about and that impedes us from picking up multinational clients.
"This is what I'm going to change."
