The terms of the deal were not disclosed.

The two firms said the terminal is being bought by Nieuport Aviation Infrastructure that includes its partners Kilmer Van Nostrand Co, the investment vehicle of billionaire investor Larry Tanenbaum; Swiss private equity firm Partners Group and a group of institutional investors advised by J.P. Morgan Asset Management.

"Billy Bishop Toronto City Airport is a highly attractive infrastructure asset in a stable market. Its close proximity to the city's business district means it is ideally positioned to continue attracting its share of the business travel market," said Todd Bright, the head of Americas Private Infrastructure investments at Partners Group, in a statement.

The airport is the ninth busiest airport in Canada, serving 2.4 million passengers in 2014.

In December, sources involved in the sale process, said the auction had attracted interest from a number of buyers including pension fund manager Alberta Investment Management Corp (AIMCo) and Macquarie Group Ltd.

Porter Aviation Holdings, the parent of upstart Canadian carrier Porter Airlines, said in August it was planning to sell and then lease back the passenger terminal to focus on its core airline business.

In 2013, Porter unveiled a plan to more than double its fleet, with a conditional order worth up to $2.08 billion for Bombardier Inc's new CSeries jets.

Nieuport Aviation was advised on the deal by BMO Capital Markets and law firm McCarthy Tétrault. The debt financing on the deal was lined up by Bank of Nova Scotia, Caisse centrale Desjardins and National Bank of Canada.

Porter's financial advisers were Barclays Capital Canada and RBC Capital Markets. Norton Rose Fulbright acted as its legal advisors on the deal.

(Reporting by Euan Rocha; Editing by Grant McCool)