The move ends a seven-year relationship between WWAV Rapp Collins Media and Legal & General.
Legal & General put the account up for review in July and appointed the AAR to create a shortlist of direct marketing specialists and media agencies to pitch for the brief.
At the time it was considered likely that Legal & General would split its media account from its creative assignment, which is also held by WAVV.
Carat takes over the account with immediate effect and will run it through its Carat Direct Communications division, headed by Helen Davies.
Legal & General has an above-the-line media budget of £5.5 million, spent largely on press advertising. It also spends a considerable amount below the line.
In November, it launched an integrated below-the-line campaign to support its "2 in 1" ISA. This campaign incorporated media including targeted inserts, national press and direct mail.