FM Environmental, based on Greenbank Industrial Estate, specialises in grease removal and water treatment systems.
Now it will supply its Grease Guardian fat removal equipment to Asda parent company Walmart, which will use it in around 200 of its in-store restaurants in Mexico.
FM Environmental, founded 35 years ago, got the help of Invest NI in its global marketing, and also took part in its international visit programme.
It already exports to over 30 markets, including the US, Great Britain, the Republic of Ireland, France and Russia, and runs a manufacturing plant in Malta.
Company marketing director Eamon Fitzpatrick said: "Winning this business from such a prestigious customer as Walmart is tremendously encouraging and will be of enormous benefit to us as we seek to grow our business in North America, now a key target market for us.
"It’s a market with huge potential for our Grease Guardian equipment because of the scale of the fast food business, particularly in the US. We are focusing significant resources there to develop opportunities that we have already identified."
He said that focusing on international markets had helped it achieve 20% growth every year over the past few years.
"Invest Northern Ireland’s encouragement and practical support, particularly through the international visit programme, have been immensely important and has enabled us to position the business for further growth in the US, Europe and the Middle East."
Invest NI trade director Dr Vicky Kell said the Mexico deal was "extremely important" for the company, and praised its commitment to growing in external markets.
"The company has developed a structured approach to its international business involving extensive market research to pinpoint opportunities. Its success is also based on fast response to initial leads supported by excellent customer service. This responsive engagement is a key requirement for successful exporting and is something many companies neglect."
FM Environmental also announced it had won the mechanical and electrical subcontract to supply and install three surface water pumping stations at Guernsey airport and its runways.