Belfast International Airport has refinanced a £30.6m loan with First Trust and moved all of its banking operations to the lender.
The airport said the new arrangement would cut down its annual charges - and that the savings would be reinvested in the business.
Managing director Graham Keddie said proposals from banks had been subject to "rigorous and critical examination".
"First Trust ticked all the boxes and we had no hesitation in selecting the bank as our new banking partner," he added.
And Des Moore, head of First Trust Bank in Northern Ireland, explained: "The airport re-financing is one of the largest financial transactions in recent times, and we're delighted to have won the business.
"The airport is a very significant employer in Northern Ireland, with further growth expected in the years ahead.
"It also plays an important economic enabler role for the wider economy.
"The business is varied and dynamic and our team is looking forward to supporting its ambitious growth plans."
Passenger numbers at Belfast International were up by 16% during April this year to 400,000, while the airport received a boost from the arrival of Ryanair in March.
According to its most recent financial results, the airport formerly banked with Bank of Ireland.
At the end of December 2014, the airport's assets were valued at £66m.