The news comes just two months after Lovefilm hired the former Sainsbury's brand marketing manager, Andrew Ground, as its UK managing director with the task of hiking its membership from 350,000 to more than one million.
TBWA\London will hope to help achieve this by creating Lovefilm's first brand campaign, which will run across TV, cinema and online, with £2.5 million assigned for the first burst of activity.
Up until Ground's appointment, Lovefilm's marketing activity had been scattered across different marketing channels and agencies.
In October, it ran a national press campaign through Barrett Cernis, which focused on the brand's passion for film.
Last year, it signed a deal with the washroom advertising company CPA to run ads in 1,000 UK locations in the run-up to Christmas. It has also partnered with Guardian Unlimited for a joint DVD-rental service for users and sponsored the Michael Powell Award at the Edinburgh International Film Festival.
Matt Shepherd-Smith, the chief executive at TBWA\London, said: "Lovefilm has a great product and will become a huge brand. We're going to have fun working together."