Morris Nicholson Cartwright previously held the account, and devised the slogan "iron age woman", to promote the clay cookers.
Aga is believed to be ploughing £1m into the new advertising campaign, in a bid to drive sales, which mainly come from high-income households. Cogent Elliott will target a younger, more urban consumer base with its advertising.
Cogent will also be tasked with marketing communications for the brand, after fending off competition from four other agencies to win the account. Direct mail, point of sale, digital consultancy and customer relationship management will all be part of the agency's remit.
Simon Page, Aga's marketing director, said: "Cogent's understanding of our strategic challenges and ability to apply outstanding creativity across the full range of media, coupled with their insight into our target market through their work with other premium brands such as Jaguar and Fortnum & Mason makes them an ideal partner."
Tim Pile, CEO of Cogent Elliott, said: "Aga is a truly iconic brand that invokes a passionate response from those involved with it -- and we're delighted to be part of the team taking that brand forward."
Cogent Elliot's head office resides in the midlands, with satellite offices in London and Danbury.