The new agency is called Seven Brands and describes itself as international and multicultural in perspective, clients and staff.
Montgomery left Futurebrand during a restructure last March that also saw the departures of managing creative director Tina Prior and head of strategy Piers Guilar.
She is a former head of branding and marketing for Singapore bank, DBS.
Grainger has worked for global companies such as Standard Chartered and GlaxoSmithKlein and worked on both the CelTel and Zain brands.
Montgomery says that the consultancy’s ambition is to put Middle Eastern, African and Asian brands on the list of top global brands over the next ten years and to work with Western companies looking east for emerging opportunities.