The agency will manage the Intercork programme that promotes cork as a superior alternative to metal screw caps on wine bottles.
Grayling's contract is overseen by Apcor, the Portuguese Cork Association, and covers six countries. In the UK and Italy, the focus will be on cork stoppers. In China, Japan, Russia and the UAE, the agency will promote cork as a building and decoration material. In the UK alone, the business is estimated to be worth more than £1m.
Apcor is responsible for 85 per cent of worldwide cork exports, and the industry represents 16 per cent of Portugal's foreign income.
'Intercork is the biggest comms project that Apcor has ever developed and therefore the choice of partner was critical,' said Apcor representative Carlos de Jesus.
'Grayling had clearly researched the markets thoroughly and the plans that the teams presented were tailored to each country.'