Carat won the business after a pitch against incumbent WWAV Rapp Collins Media, ZenithOptimedia and Initiative Media.
Legal & General's marketing director, Caroline Fawcett, said Carat's knowledge of direct marketing and its buying clout helped it win out in the contest.
Fawcett said: "All of the pitch presentations were of a very high standard, but we were particularly impressed with Carat's knowledge of the direct market, excellent buying power, solid planning skills, and creative and insightful approach to our market."
She added: "Our business model has become increasingly complex with many new routes to market, and we are confident that Carat will help us to capitalise on the opportunities that these now present."
The Legal & General win is a significant one for Carat because it lost the £27m media account for high street bank Abbey in May to MindShare. Initiative also pitched for this work.
Colin Mills, managing director at Carat, said the win was a result of a year's focus on building its direct offering.
Mills said: "Our direct communications department has been a significant area of focus for us this year. This win stands as a ringing endorsement of the team's success. Legal & General is a sophisticated marketing organisation and we look forward to helping them achieve their business objectives in the future."
The media pitch has been running alongside the pitch for the Legal & General creative account, which is also held by WWAV. Agencies believed to have pitched are CCHM, DP&A, Draft and the incumbent. The result of this pitch is not yet known.
The media and creative reviews were conducted by the AAR. The shortlist was drawn up in July and the pitches held in August.
Legal & General offers financial services including life and pension products, investments, general insurance and group risk.
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