Aegis Group has won the pan European media buying and planning account for General Motors, the world's second largest spender on advertising behind Procter & Gamble, Aegis said.
The account, which will be among Aegis's largest, is valued at about $750 million (401.8 million pounds) , according to industry sources, though Aegis will receive only a fraction of that as fees for helping GM decide where to spend its advertising budget.
Aegis declined to comment on the value of the account.
Interpublic Group of Cos. formerly held the auto maker's account, which includes the Vauxhall, Saab and Chevrolet brands. The world's third largest advertising conglomerate also lost GM's massive U.S. media buying account to Publicis last year.
Within Europe, GM is one of the largest advertisers in Britain, Spain, Switzerland and Sweden.
The account is a big win amid some controversy for Aegis, which is facing a renewed attempt from its largest shareholder, French financier Vincent Bollore, to gain seats on its board.
Bollore, who is also the chairman and top shareholder of rival ad group Havas, lost an attempt for two Aegis board seats in June, when shareholders voted against his nominees.
The UK advertising group also suspended the head of its business in central and eastern Europe and South Africa last week after German prosecutors launched an investigation following allegations of embezzlement by him and others.