This follows a two year campaign led by Fairtrade West Sussex, which was set up in 2009.
The local Fairtrade steering group, with the support of West Sussex County Council, has achieved the five criteria necessary to be granted the award.
The fundamental aim of Fairtrade is to change the way trade works through better prices, decent working conditions, and a fair deal for farmers and workers in developing countries.
It also ensures these farmers get an equal say in every trading deal.
The county council promotes a number of initiatives such as ensuring that Fairtrade tea and coffee is available in its schools and staff restaurants, together with the provision of education packs to communities.
It also collaborates with the local Fairtrade steering group to promote it amongst West Sussex businesses, commercial and other organisations, including shops and cafes.
Jeremy Hunt, cabinet member for finance and resources, said: “This is excellent news and a due reflection of the hard work put in by the Fairtrade West Sussex group.
“The county council will continue to promote Fairtrade initiatives and products to ensure more residents are aware of Fairtrade and the benefits of it.”
Sue Joy, convenor of Fairtrade West Sussex, added: “We are delighted the Fairtrade Foundation has agreed to Fairtrade county designation.
“We look forward to working in close partnership with West Sussex County Council in the future to ensure that it is known throughout the county at every level.”