In 1945, aware of the importance of aviation for the development of the economy of Puerto Rico, the island government had pointed out the need to build a newer international airport capable of handling the growing air traffic of San Juan International Airport, in Isla Grande, that had been operating since 1929. Until then, Isla Grande had been the main airport of Puerto Rico. As airlines began switching from propeller aircraft to jets, the 4,000 foot (1,200 m) Isla Grande airstrip did not have the necessary distance for modern aircraft to land and take off. 

The local government had also decided that it should direct the air operations, relying these powers in the Puerto Rico Transportation Authority, created in 1942, which later became the Ports Authority. The Committee of Airports of the Planning Board began to study the feasibility of the new airport, submitting in 1944 its plans and studies to the Federal Civil Aeronautics Administration, to determine the most appropriate place.

In 1945, it was determined that the place would be Isla Verde (Carolina), to make the airport a metropolitan facility. Construction was approved by the Puerto Rico Planning Board in 1946, and the project began in 1947. During that same year, the Port Authority of Puerto Rico assumed title to and ownership of the Isla Grande Airport and other regional airports, which had been military installations during World War II.

During 1949, the first phase of construction of the Isla Verde Airport was completed: cleaning, filling, leveling and drainage of soils. The second phase also began: paving the runway, taxiways, and platforms. On May 22, 1955, the Puerto Rico International Airport was inaugurated, built on a 1,718.72 acres (695.54 ha) land lot. The facilities, estimated at a cost of $22 million, had a six-story passenger terminal, control tower, 7,800 foot (2,400 m) long runway (8–26), cargo building, fire and police stations, and a hotel.

At the start of operations, the airport had only one runway (8/26), the old control tower on top of the hotel, 3 terminals and a parking lot for 200 cars. In the early 1960s, several expansion and improvement projects began, starting with the runway extending from 7,800–10,000 feet (2,400–3,000 m) in length. Construction of the second runway (10–28) on the south side began in May 1967. The project was completed in 1974 at an approximate cost of $4.2 million. With the introduction of the 747 aircraft, runway 8–26 was reinforced and widened in 1974, and ten years later it was repaved.

On January 17, 1983, the two-leveled vehicular access system was built. This access separates the arrivals and departures of passengers at different levels, to eliminate traffic congestion.

https://aeropuertosju.com

https://en.wikipedia.org/wiki/Luis_Mu%C3%B1oz_Mar%C3%ADn_International_Airport#History