Montgomery will be responsible for driving the London business, including overseeing the client base and product offering across brand strategy, corporate identity, consumer branding and packaging, brand environments and digital.
She joined FutureBrand in 2003 as head of strategy from DBS Bank in Singapore, where she was vice-president of group branding and marketing.
Before that Montgomery spent two years at Interbrand advising clients such as GM, Sparq, BMW and Credit Suisse.
Prior has been promoted to managing creative director with responsibility for the direction and management of FutureBrand's London office. She is also creative lead on some of the agency's largest and most longstanding accounts, including as Unilever, Nestle and CPW.
Prior joined FutureBrand from Lambie-Nairn eight months ago, where she was creative director on the O2 account.
She has also worked on the development of new brands such as Nesta (National Endowment for Science, Technology and the Arts), The CarbonNeutral Company, The Royal Landscape and Simon Westons' charity Weston Spirit.
Montgomery and Prior will report to Patrick Smith, chief executive officer of FutureBrand Europe.
Smith said: "Our London team is a well balanced mix of strategic and creative thinking that is now stronger than ever. Led by Jasmine and Tina, FutureBrand London can now expand onto an even bigger global stage."