The centralised European account takes in 13 countries, including the UK business, which is worth £40m.
The Dell win secures Carat's biggest online client across Europe and follows its recent successful retention of supermarket chain Asda. Both Dell and Asda rank in the agency's top five clients.
Carat has handled Dell's media account for the past 15 years after initially working on the UK business brief since 1991.
Dell began reviewing its European media planning and buying business two months ago, following the transfer of a slice of its creative business from DDB London to AdPeople, a Danish advertising agency.
OMD currently handles Dell's US media business after winning the account three years ago, while its Asian market is run by Havas, which won the business last year.
Founded in 1984 by Michael Dell, Dell provides global computer systems for both businesses and individual consumers.
The company established its business in the UK in 1987, initially selling and manufacturing desktop PCs. It has since introduced a wide range of hardware and software to the UK market.
Its European and EMEA headquarters are based in Bracknell, Berkshire, where the company employs more than 1,000 staff.
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