BAE Systems, Britain's biggest defence contractor, has agreed a £6bn contract to supply 24 Typhoon fighter jets to Qatar.
The deal, which will help to secure UK jobs, includes a support and training package.
It also includes an intention for Qatar to buy further military equipment from Britain, namely the purchase of Hawk aircraft.
Around 5,000 workers in the UK are employed on building the Typhoon, mainly at Warton in Lancashire.
Charles Woodburn, BAE Systems chief executive said: "We are delighted to begin a new chapter in the development of a long-term relationship with the State of Qatar and the Qatar Armed Forces, and we look forward to working alongside our customer as they continue to develop their military capability.
"This agreement is a strong endorsement of Typhoon's leading capabilities and underlines BAE Systems' long track record of working in successful partnership with our customers."
The deal was signed by Defence Secretary Gavin Williamson and his Qatari counterpart Khalid bin Mohammed al-Attiyah.
A statement from Qatar's armed forces said the two ministers also signed an "agreement for building up a Joint Operational Squadron" between the two countries' air forces to provide security during the 2022 football World Cup, which the Gulf state is hosting.
Mr Williamson said the contract is the biggest export agreement for the Typhoon in a decade and "will boost the Qatari military's mission to tackle the challenges we both share in the Middle East".
He added: "As we proudly fly the flag for our world-leading aerospace sector all over the globe this news is a massive vote of confidence, supporting thousands of British jobs and injecting billions into our economy."
Qatar is the ninth country to sign a deal for Typhoon jets, with delivery expected to commence in late 2022.
The announcement comes as the Government searches for major global trade deals amid Britain's withdrawal from the European Union.
Last week Prime Minister Theresa May struck a deal with Brussels after the first phase of Brexit negotiations, in the hope of talks progressing on to trade.
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