The account was previously with Text100, which inherited Diet Coke as a client when it merged with Lexis in 2017. Lexis won the business from Cohn & Wolfe in 2003.
Coca-Cola declined to provide any further details about the pitch process as it typically does not comment on agency reviews.
However, the drinks company did stress that it will continue working with Text100 on other brands.
Frank founder and managing partner Andrew Bloch told PRWeek that he was delighted with the win, which he described as dream brand and client for the agency.
The Diet Coke account continues a streak of recent wins for Frank in the past few months, including Huawei and Rimmel London.
The agency recently lost US brewer Scofflaw following a furore surrounding a ‘rogue’ press release.
Recently, Coca-Cola retained MediaCom as its media agency, while earlier this year Diet Coke released several new flavours.
