Candler Field/Atlanta Municipal Airport (1925–1961)

Hartsfield–Jackson began with a five-year, rent-free lease on 287 acres (116 ha) that was an abandoned auto racetrack named The Atlanta Speedway. The lease was signed on April 16, 1925, by Mayor Walter Sims, who committed the city to develop it into an airfield. As part of the agreement, the property was renamed Candler Field after its former owner, Coca-Cola tycoon and former Atlanta mayor Asa Candler. The first flight into Candler Field was September 15, 1926, a Florida Airways mail plane flying from Jacksonville, Florida. In May 1928, Pitcairn Aviation began service to Atlanta, followed in June 1930 by Delta Air Service. Those two airlines, later known as Eastern Air Lines and Delta Air Lines, respectively, would both use Atlanta as their chief hubs. The airport's weather station became the official location for Atlanta's weather observations on September 1, 1928, and records by the National Weather Service.

Atlanta was a busy airport from its inception, and by the end of 1930, it was third behind New York City and Chicago for regular daily flights with sixteen arriving and departing. Candler Field's first control tower opened March 1939. The March 1939 Official Aviation Guide shows 14 weekday airline departures: 10 Eastern and four Delta.

In October 1940, the U.S. government declared it a military airfield and the United States Army Air Forces operated Atlanta Army Airfield jointly with Candler Field. The Air Force used Hartsfield–Jackson primarily to service many types of transient combat aircraft. During World War II, the airport doubled in size and set a record of 1,700 takeoffs and landings in a single day, making it the nation's busiest in terms of flight operations. Atlanta Army Airfield closed after the war.

In 1942, Candler Field was renamed Atlanta Municipal Airport and by 1948, more than one million passengers passed through a war surplus hangar that served as a terminal building. Delta and Eastern had extensive networks from ATL, though Atlanta had no nonstop flights beyond Texas, St. Louis, and Chicago until 1961. Southern Airways appeared at ATL after the war and had short-haul routes around the Southeast until 1979.

In 1957, Atlanta saw its first jet airliner: a prototype Sud Aviation Caravelle that was touring the country arrived from Washington, D.C. The first scheduled turbine airliners were Capital Viscounts in June 1956; the first scheduled jets were Delta DC-8s in September 1959. The first trans-Atlantic flight was a Delta/Pan Am interchange DC-8 to Europe via Washington starting in 1964; the first scheduled international nonstops were Eastern flights to Mexico City and Jamaica in 1971–72. Nonstops to Europe started in 1978 and to Asia in 1992–93.

Atlanta claimed to be the country's busiest airport, with more than two million passengers passing through in 1957, and, between noon and 2 p.m. each day, it became the world's busiest airport. (The April 1957 OAG shows 165 weekday departures from Atlanta, including 45 between 12:05 and 2:00 PM and 20 between 2:25 and 4:25 AM.) Chicago Midway had 414-weekday departures, including 48 between 12:00 and 2:00 PM. In 1957, Atlanta was the country's ninth-busiest airport by flight count and about the same by passenger count.

Original jet terminal (1961–1980)

In late 1957, work began on a new $21 million terminal, which opened on May 3, 1961. In 1960, the City of Atlanta annexed the area surrounding the new terminal. Consisting of six pier-style concourses radiating from a central building, the terminal was then the largest in the country and could handle over six million travelers a year; the first year, 9.5 million people passed through. In March 1962, the longest runway (9/27, now 8R) was 7,860 feet (2,400 m); runway 3 was 5,505 feet (1,678 m) and runway 15 was 7,220 feet (2,200 m) long.

In 1971, the airport was named William B. Hartsfield Atlanta Airport in honor of Atlanta mayor William B. Hartsfield after his death. The name change took effect on February 28, 1971, which would have been Hartsfield's 81st birthday. The new name would be relatively brief, as it would be changed later in 1971 to William B. Hartsfield Atlanta International Airport with the growth of flights to and from Atlanta outside North America.

Midfield terminal (1980–present)

To address the significant increase in air traffic that outstripped the capacity of the 1961 terminal, and after years of planning and design, construction began on the present midfield terminal complex in 1977 under the administration of Mayor Maynard Jackson. It was billed as the largest construction project in the South, costing $500 million. The complex was designed by Stevens & Wilkinson, Smith Hinchman & Grylls, and Minority Airport Architects & Planners. The new complex — initially consisting of the North and South Terminals, Concourses A through D, and the northern half of the present-day Concourse T (which served as the International Terminal) — opened on September 21, 1980, on time and under budget. It was designed to accommodate up to 55 million passengers per year and covered 2,500,000 square feet (230,000 m2).