Airbus has acquired a majority stake in Bombardier's C Series aircraft programme, the companies have announced.
The move has been hailed as a "positive step forward" by Business Secretary Greg Clark and comes after the US government proposed a 300% duty on exports of the planes to the US amid an international trade dispute.
DUP leader Arlene Foster said it was "significant news" for Bombardier, which employs more than 4,000 people at its Belfast factories and is due to begin delivering a blockbuster order for up to 125 new C Series jets to Atlanta-based Delta Airlines next year.
Airbus has obtained a 50.01% stake in the C Series Aircraft Limited Partnership and the deal will help improve sales.
Airbus chief executive Tom Enders said: "Not only will this partnership secure the C Series and its industrial operations in Canada, the UK and China, but we also bring new jobs to the US."
Bombardier president Alain Bellemare said: "This partnership should more than double the value of the C Series programme and ensures our remarkable game-changing aircraft realises its full potential."
Last month, the US Department of Commerce (DoC) announced it would impose an interim tariff of nearly 220% on the jets - with unions warning the move could cost jobs in Belfast.
A second preliminary levy of 80% has been loaded on the sales of Canada-based Bombardier.
Announcing the regulator's preliminary finding, US secretary of commerce Wilbur Ross said the subsidisation of goods by foreign governments was something that the president's administration "takes very seriously".
Bombardier labelled the determination "absurd", while in its response the UK Government said the statement was "disappointing" and pledged to defend UK interests "at the very highest levels".
Speaking about the Airbus-Bombardier deal, Mr Clark said: "Since Boeing initiated action against Bombardier, we have been active alongside our Canadian counterparts to work to secure the future of the C Series and safeguard jobs and manufacturing at Bombardier Shorts in Belfast, and the supply chain across the UK.
"We will continue to work closely with the companies to protect UK interests and with the Canadian government to ensure the unjustified case brought by Boeing is brought to a swift resolution.
"There is some way to go before the deal is completed and our number one priority throughout will be the workforce in Northern Ireland."
Davy Thompson, regional officer of Unite, welcomed the news.
He said: "We have received assurances that this will mean that employment associated with the manufacture of C Series wings will remain in Belfast.
"This deal, which will see Airbus take on responsibility for procurement, sales and marketing and customer support expertise, has the potential to open the door to new markets and ensure long-term sustainability of C Series production, despite the ongoing difficulties experienced with onerous tariffs being imposed on the company by a protectionist United States.
"The agreement will allow Bombardier to leverage Airbus's global scale and reach, and open access to their supply chain.
"Unite will continue our efforts to ensure the withdrawal of the US tariffs on the C Series but this is a welcome development - one that gives breathing space to the C Series itself and which we anticipate should safeguard the future of C Series production jobs in Belfast for the foreseeable future.
"While we welcome this announcement in regard to the C Series, there are continued challenges associated with employment on other Bombardier contracts in Belfast, we will be engaging with management and our membership to safeguard all workers' interests in the coming period."