Purdon will join the agency on 21 February and her remit will include winning new clients.
She was formerly business development manager (EMEA) at business travel network Whenthemeetingsover.com.
Monica Lee has also been appointed as a project manager, joining the delegate management team to work on global investigator meetings for key pharmaceutical clients.
Lee was previously international travel and event manager at GDS International.
Five Hats managing director David Waldman said: "Five Hats has grown steadily and organically since its inception in 2006 and Caroline and Monica join us at an exciting time."