The original airfield was established in 1920 as Hamilton Airport by local business owner and aviator, Thomas F. Hamilton. Milwaukee County purchased the land on October 19, 1926, and renamed the airport Milwaukee County Airport. The first airport terminal there, the Hirschbuehl Farmhouse, opened in July 1927. That month, Northwest Airlines, Inc., began air service from Milwaukee to Chicago and Minneapolis/St. Paul. In August 1927, world-renowned aviator Charles Lindbergh visited the Milwaukee airport. Kohler Aviation Corporation began providing passenger service across Lake Michigan on August 31, 1929.

During the late depression years (1938–July 1940), a new two-story passenger terminal building was constructed by the Works Progress Administration. On March 17, 1941, the airport was renamed General Mitchell Field after Milwaukee native and air power advocate Brigadier General William "Billy" Mitchell. On January 4, 1945, Mitchell Field was leased to the War Department for use as a World War II prisoner-of-war camp. Over 3,000 prisoners and 250 enlisted men stayed at the work camp. Escaped German prisoners were often surprised to find a large German American population just beyond the fence.

The present terminal opened on July 20, 1955, and was designed by Leigh Fisher and Associates. It was renovated and expanded in 1985, designed by Miller, Meier, Kenyon, Cooper Architects and Planners Inc. The "hammerhead" section of the D concourse was added in 1990.

On June 19, 1986, the Milwaukee County Board of Supervisors renamed the airport General Mitchell International Airport. The airport was formerly a hub for AirTran Airways, Frontier Airlines, Midwest Airlines and North Central Airlines. The airport is owned and operated by Milwaukee County, but some Milwaukee business leaders and politicians have advocated privatization or leasing it to a third party for financial reasons.

In February 2019, the airport was renamed from "General Mitchell International Airport" to "Milwaukee Mitchell International Airport," a rebranding meant to highlight the airport's location; the old name is still used by the FAA and US government.

Expansion

Mitchell International expanded the runway safety area at the end of the runways after an accident on January 21, 2007, when Northwest Airlines Flight 1726 skidded off the runway following an aborted takeoff. According to the FAA, most airports are encouraged to have a runway safety area no shorter than 1,000 feet (305 m), though many airports do not. Construction of the runway safety areas began at the end of summer 2009 and was completed in fall 2012.

There was also a "Master Plan" idea to increase the terminal area by stretching the existing terminal (in some cases, to almost double the size) or begin construction of a separate terminal. Nearly all cases would involve major reconstruction on the airport itself, and would have a huge impact on the airport's traffic. These plans were, however, drafted before Mitchell saw a significant reduction in carriers and flights. More recently, in 2012, there were discussions of closing one concourse as a cost-cutting move.

The approved 2018 Milwaukee County Budget contained initial funding for replacement of the now-closed Concourse E with a new International Terminal. It would replace the current International Arrivals Terminal (IAT) which has limited capacity and is not connected to the main terminal building. The new terminal was planned to open in 2020 after the demolition of Concourse E was completed. During October 2018, airport and Milwaukee County officials set a timeline for design, construction and completion of the new International terminal. Pre-design work and bidding concluded in November 2018, with construction set to begin in early 2021 and likely concluding in mid-2022. In May 2020, Milwaukee County announced with the COVID-19 pandemic severely reducing the airport's operations and de facto ending international service temporarily, that the start of the project had been postponed.

As of September 2025, work has started on the redevelopment of Concourse E to build a new international concourse. This will allow the closure of the existing International Arrivals building, which is currently separate from the main terminal. Airport officials are expecting to conclude the project in 2027.