The 12-month PR programme will be managed from Grayling's London office, with a particular focus on the UK, Europe, the Middle East and Latin America.
Grayling has been charged with raising the profile of the business in these key markets as well as handling day-to-day media relations activity.
The specialist institution provides banking services to the high-net-worth individuals.
Michael Murphy, CEO of Grayling, said: 'The appointment reinforces our ability to conduct integrated public relations programmes on a global scale by linking "on-the-ground" country teams with central co-ordinating resources. We are excited to play a key role in supporting the bank in raising its profile on a global scale.'
Grayling launched as a unified consultancy in January 2010 after parent Huntsworth brought together Grayling with Trimedia, Mmd and a number of its smaller brands.