Airbus has acquired a majority stake in Bombardier's C Series aircraft programme, the companies have announced.
The European company obtained a 50.01% stake in the project, which has been faced with the US government imposing a 300% duty on exports of the plane to the US, amid an international trade dispute.
Theresa May previously vowed to work to protect jobs in Northern Ireland following the potentially crippling impact of the tariff.
Bombardier employs more than 4,000 people at its Belfast factories and is due to begin delivering an order for up to 125 of the new jets to Delta Airlines next year.
DUP leader Arlene Foster said Airbus's involvement was "significant news", while the business secretary Greg Clark hailed the move as a "positive step forward", adding: "I think there is great excitement that this could be an expansion of the prospects for jobs in Belfast."
Airbus CEO 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 the Canadian-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".