The airfield was built in 1939 during the Japanese Imperial period as an Imperial Army base. The runways were built on a bed of rocks manually hauled by Korean labourers from Kaihwasan and Yangchan, several miles from the base. Then known as Keijo New Airfield (京城新飛行場), Gimpo was constructed with four runways to supplement the much smaller Keijo Airfield (京城飛行場), which was later known as Yeouido Airport.

Korean War

Gimpo played a major role during the Korean War, and the USAF designated the airfield as Kimpo Air Base or K-14.

North Korean forces attacked South Korea on 25 June 1950 starting the Korean War. During one of the first Korean People's Air Force (KPAF) attacks on 25 June, a Military Air Transport Service C-54 Skymaster was destroyed on the ground at Gimpo. On 27 June, US naval and air forces began evacuating 748 US diplomats, military dependents, and civilians by air transport from Kimpo and Suwon Airfield. On the afternoon of 27 June, five F-82 Twin Mustangs of the 68th Fighter Squadron and 339th Fighter Squadron were escorting four C-54 Skymaster aircraft out of Kimpo when the C-54s were attacked by five KPAF Lavochkin La-7 fighters. In the subsequent dogfights, three LA-7s were shot down for the loss of no US aircraft in the first air battle of the war. Later that day, four F-80Cs of the 35th Fighter-Bomber Squadron shot down four Ilyushin Il-10s for no losses over Gimpo in the USAF's first jet-aircraft victory.

Gimpo was captured by the KPA shortly after the capture of Seoul on 28 June 1950. On 29 June, eight B-29s of the 19th Bomb Group bombed Gimpo and the Seoul railyards. By July, the KPAF were using the base for attacks on UN forces; on 10 July, seven Yak-7s were hidden at Gimpo and used in strikes against UN positions at Cheongju. The next day, they surprised and damaged several F-80s in the area. On 15 July, the US launched an attack on Gimpo, destroying two or three of the seven Yak-7s there and damaging the runway. On 5 August 5th Air Force fighters strafed and bombed Gimpo, destroying 9 aircraft and damaging 9 others.

Following the Inchon landings on 15 September 1950, the 2nd Battalion 5th Marines was ordered to seize Gimpo on 17 September. Gimpo was defended by a conglomeration of half-trained fighting men and service forces, and by the morning of 18 September, the Marines had secured the airfield. The airfield was in excellent shape as the North Koreans had not had time to do any major demolition. On 19 September, the U.S. Army Corps of Engineers repaired the local railroad up to 13 kilometres (8 mi) inland and 32 C-54 transport planes began flying in gasoline and ordnance. VMF-212 was one of the first units to operate from Gimpo before moving forward to Yonpo Airfield. On 25 September, the 811th Engineer Aviation Battalion began repairing bomb damage on the 1,800-metre (6,000 ft) asphalt runway at Gimpo and covering it with Marston Matting. On 6 October, the USAF took control of Gimpo from the USMC.

On 20 December 1950 Gimpo was the scene of the "Kiddy Car Airlift", the rescue of 964 orphans and 80 orphanage staff from Seoul in the face of the advancing Chinese People's Volunteer Army (PVA).

On 31 December 1950 the PVA attacked the UN forces north of Seoul. On 2 January 1951 the 4th Fighter-Interceptor Wing withdrew from Gimpo to bases in Japan. On 3 January UN forces withdrew from Seoul and on 4 January USAF engineers destroyed stocks of fuel and munitions and some of the buildings at Gimpo, before abandoning the base.

UN forces resumed the offensive again in late January 1951 and launched Operation Thunderbolt on 25 January, with the aim of pushing Chinese and North Korean forces back north of the Han River. By 10 February 1951, UN forces once again had control of Gimpo.

USAF units based at Gimpo included:

51st Fighter-Interceptor Wing from 6 October-December 1950

4th Fighter-Interceptor Wing (initially the 336th Fighter-Interceptor Squadron equipped with F-86A Sabres) December 1950 and August 1951 onwards

8th Fighter-bomber Wing from June-August 1951

67th Tactical Reconnaissance Wing from August 1951

606th Aircraft Control and Warning Squadron from July 1951

On 21 September 1953 KPAF Lieutenant No Kum-Sok defected, landing his MiG-15 at Gimpo.

International era

In 1958, the airport was redesignated as the Gimpo international airport of Seoul by a presidential decree, completely replacing the existing Yeouido Airport.

Eventually, the South Korean government decided to build a new airport. The facility was initially planned to be in Cheongju, 124 kilometres (77 mi) away from Seoul, but that idea was strongly opposed by the citizens of Seoul and Gyeonggi Province, due to the inconvenience it would pose to them. (It would have been farther from Seoul than the 80 kilometres (50 mi) distance between Viracopos Airport in Campinas, Brazil, and the city of São Paulo.) Finally, Yeongjong Island, a part of the city of Incheon, slightly west of Seoul, was chosen for the new airport, which later came to be known as Incheon International Airport.