The account, which was previously held by Propaganda, was put up for pitch in November last year, with eight agencies in the fray.
BDH\TBWA will be responsible for all of the company's brand communications, as it looks to expand globally.
This will include a strong focus on experiential marketing, events and PR, as well as TV and print campaigns, and will be promotion-led, rather than brand-led.
Robert Harwood-Matthews, the chief executive of BDH\TBWA, said: "GHD is a fantastically sexy, ambitious and creative brand."
Martin Penny, the managing director of GHD, added: "We are very excited about moving forward with BDH\TBWA. It will give us the additional support we need with our global expansion plans."