1917–1945

The airport lies within the parish of Killead, between the small villages of Killead (to the east) and Aldergrove (to the west). The site for the airport was established in 1917, when it was selected to be a Royal Flying Corps (RFC) training establishment during the First World War. The airport remained open at the end of the war for RAF activity.

Civil traffic began in 1922, when flights were conducted to fly newspapers from Chester. The first scheduled passenger service was started in 1933 by the Scottish airline Midland & Scottish Air Ferries. This service consisted of two daily flights each way between Aldergrove and Renfrew Airport, Glasgow. This was subsequently augmented by a twice-daily, return service to Croydon, at that time London's airport, with stops at the Isle of Man, Liverpool and Birmingham.

During the Second World War, Aldergrove remained an RAF station particularly for the Coastal Command. So that the airport could accommodate larger, long-range aircraft, a major works programme was undertaken to replace the four existing runways with two new long paved runways, thereby forming the basis of the layout that still exists at the airport today.

1946–1970

One of the outcomes of the wartime airfield construction programme was the building of Nutts Corner Airport, just 3 mi (4.8 km) from Aldergrove. On 1 December 1946, the new site replaced Belfast Harbour Airport (now George Best Belfast City Airport) as Northern Ireland's civil airport, as the Harbour Airport was considered unsuitable.

By the 1950s civil air traffic had outstripped the facilities at Nutts Corner and aircraft were being regularly diverted to Aldergrove because of adverse weather conditions. In July 1959 the decision was made to move civil flights to Aldergrove to take advantage of the large airfield and this took place in October 1963.

A new terminal and apron were built, with the necessary passenger facilities, and the complex was opened by Queen Elizabeth The Queen Mother on 28 October 1963. The first regular jet service to London–Gatwick started in 1966, and in 1968 Aer Lingus and BOAC introduced scheduled services to New York City via Shannon and Prestwick respectively.

1971–1999

In 1971, Northern Ireland Airports Limited was formed to operate and develop the airport and its facilities. A major programme of airfield upgrades was undertaken, resulting in improvements to runways, taxiways and the parking apron.

A new International Pier was built together with lounge facilities and car parks, while an additional apron was provided to separate the smaller general aviation aircraft from large commercial jets. In the meantime, British Airways launched the first Belfast to London–Heathrow shuttle service and the first Boeing 747 operated from the airport on a charter service to Toronto via Shannon. The first scheduled service to a European city was started by NLM Cityhopper (now KLM Cityhopper) flying to Amsterdam.

In 1983 the airport, renamed Belfast International, was regularly accommodating the largest civil aircraft in service and with the installation of new technology was capable of all-weather operations. In 1985, passenger numbers reached 1.5 million and British Midland International (BMI) went into competition with British Airways on the London–Heathrow service. Further developments to the terminal occurred throughout the late 1980s and early 1990s, extending the terminal's landside and airside area. A new Executive Aviation Terminal was also opened in 1987 and the new cargo centre opened in 1991.

The airport was privatised in 1994. TBI became the new owner of the airport on 13 August 1996, by which time annual passenger numbers had reached 2.5 million.

In 1998, easyJet started operations from the airport with flights to London–Luton. Since then the airline has established a large base at Belfast International and a further twelve domestic routes and twenty-three direct European scheduled routes have been added to the network, making the airline the largest user of the airport.

Development since 2000

In 2005, Continental Airlines launched the first ever nonstop scheduled service to Newark; this continued to operate under the United Airlines brand until the route's termination in January 2017.

In July 2013, it was confirmed that abertis would sell Belfast International Airport, Stockholm Skavsta Airport & Orlando Sanford International Airport to ADC & HAS based in the United States. In February 2015 the airport re-opened the viewing gallery that had been closed for 10 years which provides a view of the apron and the runways that serve the airport. It also includes live ATC, arrival and departure boards, and a live flight radar screen. However, this was later closed again in October 2019.

In 2014, news emerged of talks between the airport and Turkish Airlines. This could have led to a service linking Belfast into the worldwide Turkish route network, but did not materialise.

From 2015, Virgin Atlantic offered weekly services to Orlando using Boeing 747-400 aircraft with occasional services provided by the airline's Airbus A330 fleet.