The review, which will be handled by the AAR, follows the appointment of the former BBC marketer Jane Scott as the channel's director of marketing in June.
Over the past four years, TBWA's work for five has included a poster campaign to promote a documentary on Michael Jackson's cosmetic surgery.
The campaign received a gold at the Campaign Poster Awards in 2003.
TBWA was also responsible for five's current branding, which was introduced when the broadcaster changed its name from Channel 5 in 2002.
Scott said: "We have developed our new brand strategy and are now looking to refresh our creative work to reflect this change."
Five is currently running advertising including posters that promote the US medical drama House and others that advertise the forthcoming prison drama Prison Break.
Scott joined the broadcaster last June from the BBC, where she was the controller of TV marketing, strategy and development.
Her arrival at five triggered speculation that the broadcaster would review its advertising agency arrangements.
TBWA has suffered a series of account losses over the past 12 months.
Ask.com, Thomas Cook, French Connection, News International and Abbey have all taken their business out of the agency.
The review does not affect five's media agency, Vizeum.