Saudi Arabia's national airline has ordered up to 26 new aircraft from Bombardier Aerospace in a deal worth at least 1.2 billion US dollars (£733 million).
SaudiGulf Airlines has agreed to buy 16 CSeries planes, which are partly built in Belfast. An additional 10 jetliners could follow, bringing the total investment to almost two billion dollars (£1.2bn).
The newly-launched carrier has become the third CSeries customer from the Middle East.
Mike Arcamone, president of Bombardier Commercial Aircraft, said: "We have long been noting that the CSeries aircraft is attracting progressive airlines that are keen on opening new markets and operations.
"We are thrilled that SaudiGulf Airlines, based in the largest Arab economy - and one with an under-served air travel market - will base the core of its business plan on the CSeries aircraft.
"In addition to supporting SaudiGulf Airlines in the region, the CS300 aircraft will allow for growth into new markets such as the Indian subcontinent and parts of Europe, as the airline seeks to expand its network and give passengers the latest in cabin comfort."
Bombardier's new 600,000-square-foot factory in Belfast is producing wings for the CSeries aircraft, which had its successful maiden flight last year.
The wings are made using an innovative carbon-fibre composite technology developed by Bombardier engineers in Northern Ireland. This technology enables material and aircraft weight savings, which reduces manufacturing times and fuel used.
Sheikh Tariq Al Qahtani, chairman of SaudiGulf Airlines, said more than 54 million people moved through Saudi Arabia's airports last year.
"We are very excited about the CSeries aircraft's suitability for this market and the long-term success it will bring to the region," he said.
"With its clean-sheet design, modern technologies and competitive costs, the CSeries aircraft will give us the opportunity to introduce a new, quality, premium airline and an economically sustainable business model in Saudi Arabia, serving the domestic market, the Gulf and Middle East.
"SaudiGulf's CSeries aircraft will offer wide and comfortable, leather seats, and in-flight entertainment in first-class, as well as economy-class seats."