Mark White, interim chief executive of Five, said the broadcaster remained "happy" with its current media planning and buying agency Vizeum.
The move comes as Five puts its planned refresh of the core TV channel on hold until "late summer" following the recent shake-up of its management team.
In April, Five had said that, following the rebranding of Five Life to Fiver, it would turn its attention to core channel Five to give it a "brighter, lighter look".
Five Life had a more radical overhaul in April, with an attempt to position Fiver as a younger channel featuring new acquisitions and commissions including Generation Sex, Celebrity Rehab, Dirt, Sex and the City and Ocean Force.
Carl Ratcliff, Five's head of brand strategy and marketing, said Grey has an "open culture that puts the client right at the heart of the creative process".
Grey will work with Five's creative teams to refresh all of the Five brands. VCCP has worked for Five for the past two years.
Grey London's clients include P&G, GlaxoSmithKline, IPC Media, the British Heart Foundation, Dairy Crest, Eurosport, Visa and Toshiba.
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