In the 1920s, the Newark area, was the site of two airfields: Heller Field, which opened in 1919, and Hadley Field, which opened in 1924, that were used by the United States airmail service. Heller Field was the first official postal field for dedicated mail service in the United States.

In May 1921, Heller Field was closed and all air mail services moved to Hadley Field, which by 1927 also served four airlines. The U.S. Postal Service, however, desired to have an airfield closer to New York City. In 1927, people and organizations, both national and local in scope, began calling for a new airport in the area of Newark, including Newark's mayor, Thomas Raymond.

On August 3, 1927, Raymond ordered plans for a new airport. Construction, which was estimated to cost $6 million (equivalent to $111,206,897 in 2025), began on April 1, 1928, along US Route 1 and Port Newark. The construction involved a land reclamation project to create 68 acres (28 ha) of level ground, 6 feet (1.8 m) above sea level to prevent flooding, upon which a 1,600-foot (490 m) runway was to be laid. In addition to the 6,735,000 cubic yards (181,800,000 ft3; 5,149,000 m3) of earth required for the reclamation, 7,000 Christmas trees and 200 bank safes donated by a local junk vendor were used.

The airport opened on October 1, 1928, dubbed the Newark Metropolitan Airport. It was the first major airport to serve the New York metropolitan area, the first commercial airport in the United States and the first with a paved airstrip. The first lease for space at Newark Airport was signed by Canadian Colonial Airways in April 1928.

The nation's first air traffic control tower and airport weather station opened at Newark in 1930. The Art Deco style Newark Metropolitan Airport Administration Building (Building 51), adorned with murals by Arshile Gorky, was built in 1934 and dedicated by Amelia Earhart in 1935. It was the first passenger terminal in the United States and featured the nation's first air route traffic control center (ARTCC). It served as the terminal until the opening of the North Terminal in 1953.

Construction of the Brewster Hangar began in 1937 and continued through 1938. This hangar was the most advanced of its time. It was added to the National Register of Historic Places in 1979 and is now a museum and Port Authority Police headquarters.

Despite these innovations, critics said the airport was poorly designed because there was no separation of incoming and outbound passengers and no thought given to future expansion, though this did not stop Newark from being the busiest commercial airport. United Airlines, American Airlines, Eastern Airlines, and TWA signed 10-year leases with the airport that ended in 1938. Then they would pay on a month-to-month basis until LaGuardia Airport opened in December 1939; by the middle of 1940, all passenger airlines had left Newark, no longer making it the world's busiest airport.

World War II

When the United States joined World War II in late 1941, the field was closed to commercial aviation, and it was taken over by the United States Army for logistics operations. The growing importance of supplying the overseas air forces and the need for more efficient control of supply shipments led to the activation of the Atlantic (and the Pacific) Overseas Air Service Commands on October 1, 1943. With headquarters at Newark, New Jersey (and Oakland, California for the Pacific Command), the Atlantic Overseas Air Service Command exercised control over the movement of Air Corps cargo through the ports of embarkation on the Atlantic and Gulf coasts.

In 1945, captured German aircraft brought from Europe on HMS Reaper for evaluation under Operation Lusty were off-loaded at Newark, and then flown or shipped to Freeman Field in Indiana, or Naval Air Station Patuxent River in Maryland.

Reopened

The airlines returned to Newark in February 1946, when it was reopened to commercial service. In 1948, the city of Newark leased the airport to the Port of New York Authority, now the Port Authority of New York and New Jersey. As part of the lease agreement, Port Authority took operational control of the airport and began investing heavily in capital improvements, including new hangars, a new terminal, and runway 4/22.

On December 16, 1951, a Miami Airlines C-46 bound for Tampa, lost a cylinder on takeoff from runway 28 and crashed in Elizabeth, killing 56. On January 22, 1952, an American Airlines CV-240 crashed in Elizabeth while on approach to Runway 6, killing all 23 aboard and seven on the ground. On February 11, 1952, a National DC-6 crashed in Elizabeth following takeoff from runway 24, killing 29 of 63 on board and four on the ground.

Following these accidents, Newark was temporarily closed in February 1952. Most of Newark Airport's traffic shifted to Idlewild, today known as John F. Kennedy International Airport, with the remaining traffic shifted to LaGuardia Airport. These moves allowed planes to takeoff and land over the water rather than over the densely populated areas surrounding Newark Airport.