The appointment ends a concerted search for a top manager capable of pulling Bates together and ending its New York office's dismal record as a conduit for global business into the network.
Hearn's hiring will be seen as Cordiant's attempt to show that it is resolving perceived shortcomings in its senior management in advance of the publication of its expected gloomy financial results.
Hearn is a former senior manager at Procter & Gamble, Smiths Crisps, Pepsi-Co and the one-time head of United Biscuits' European snack foods division.
Last year he resigned as the chief executive of Goodman Fielder, the largest food group in Australia.
He is also a one-time Bates client, with the Australian agency George Patterson Bates having handled Goodman Fielder's Meadow Lea and Buttercup brands.
Michael Bungey, the chief executive of Cordiant, said: "Our business is now far wider in direction and scope than just advertising and in David we have someone who has not only spent a large proportion of his time in some of the world's best consumer companies, but has always been close to the ad business."
Bungey announced in September 2000 that he would be stepping down as the Bates worldwide chief executive to concentrate on Cordiant and appointed Bill Whitehead, the network's North American chief, as worldwide chief operating officer.
But the appointment of a successor was put on hold while Cordiant addressed its pressing financial problems.
Hearn announced his intention to quit Goodman Fielder at the beginning of last year.
"Bates is one of the world's great advertising and marketing brands and it's my job to see the world's multinationals recognise this,
he said.
Bungey commented: "It's no secret that we have less global business than our competitors and we need more."