As of 2022[update], 31 airlines operate at Sea–Tac, serving 91 domestic and 28 international destinations in North America, Oceania, Europe, the Middle East, and Asia.

A site near Bow Lake was chosen in 1942 and construction began the following year with funding from the federal government, Port of Seattle, and the City of Tacoma.

[citation needed] Several major concourse expansions and renovations were initiated in the 2010s to accommodate passenger growth at Sea–Tac, which had become a new hub for Delta Air Lines.

The City of Tacoma provided $100,000 towards the airport's construction costs as part of a deal for the Bow Lake site, centered around an existing private airfield plagued by heavy fog.

[12] A proposal to rename the airport for Boeing president Philip G. Johnson shortly after his death in September 1944 was rejected by Port of Seattle commissioners due to the objections of Tacoma.

The first ceremonial landing at Seattle–Tacoma Airport was made on October 31, 1944, by a United Air Lines DC-3 carrying local elected officials and civic leaders.

[15] The first commercial flights launched in May 1945 with Northwest Airlines, but use was limited due to the U.S. Army Air Force's need for the airport to stage Boeing B-29 bombers for delivery.

Various airlines had irregular flights to the airport, which used a Quonset hut with limited heating as a terminal until a permanent building was financed by a bond issue that voters approved in 1946.

[17] The terminal at the renamed Seattle–Tacoma International Airport was formally dedicated by Governor Arthur Langlie on July 9, 1949, in front of a crowd of 30,000 spectators.

[18] The 71,000-square-foot (6,600 m2) building, designed by architect Herman A. Moldenhour, included a rooftop control tower and glass courting walls in the concourses.

[23] Several projects were completed by 1961 to prepare for the Seattle World's Fair the following year, including a runway extension over South 188th Street, which was placed in an automobile tunnel that opened in July 1961.

[24][25] During construction of the runway extension in February 1961, the fossilized skeleton of a Megalonyx jeffersonii giant sloth was discovered and excavated for display at the Burke Museum in Seattle.

It added eight gate positions, bringing the total to 19, a 12,000 square feet (1,100 m2) area housing international arrivals and the offices of U.S. Customs, Immigration, Public Health and the Department of Agriculture.

[24] The Port embarked on a major expansion plan, designed by The Richardson Associates[30] and lasting from 1967 to 1973, adding a second runway, a parking garage, two satellite terminals and other improvements.

[36][38] In the late 1980s, the Port of Seattle and a council representing local county governments considered the future of air traffic in the region and predicted that the airport could reach capacity by 2000.

Members of the community opposed a third runway, as did the Highline School District and the cities of Des Moines, Burien, Federal Way, Tukwila, and Normandy Park,[40] but a 1994 study concluded there were no feasible sites for an additional airport.

[49] The Port of Seattle initially looked at simply updating the terminal in a project it called the North Satellite Renovation Plan (NorthSTAR).

The project's first phase, dedicated on July 11, 2019, expanded the terminal to the west by 240 feet (73 m) and added eight gates, a mezzanine level with eateries, and a rooftop lounge for Alaska Airlines.

[58] The airport's digital infrastructure, including its website, phone lines, check-in system, and automated baggage sorting, was disabled by a cyberattack on August 24, 2024.

[61] The growth has been partly fueled by the nationwide expansion of Seattle-based Alaska Airlines and by Delta Air Lines setting up a major international hub at SEA Airport.

[52][63] With estimates that the Puget Sound region will grow by another one million people by 2035, the Port of Seattle began developing the Sustainable Airport Master Plan (SAMP) in 2018 to meet passenger and cargo demands.

The SAMP recommends more than 30 projects to improve efficiency and airport access, including a new terminal with 19 gates and an automated people mover through three separate stations.

[65] A four-story addition to the existing structure of Concourse C began in 2023 and is scheduled to be completed in 2027 at a cost of $399 million; it includes a "central gathering place" under a large wooden ceiling.

[72] The airport began using a virtual queuing program, called SEA Spot Saver, in 2021 to reduce wait times and control crowds at security lines.

[72] The Port of Seattle maintains and curates a collection of public artwork at Sea–Tac that began with acquisitions in 1968 and was formalized with a percent for art ordinance passed in 2000.

[81] The FAA issued an alert notice dated from August 27, 2009, to September 24, 2009, urging airplanes about taking precautions such as REILs and other visual cues while landing from the north.

[88] The airport is served by the 1 Line of Sound Transit's Link light rail system at the SeaTac/Airport station with frequent service to downtown Seattle and the University of Washington.

[89] Another pedestrian bridge over International Boulevard is used to access the city of SeaTac, nearby airport hotels, and King County Metro buses including RapidRide A Line.

Sound Transit buses offer service to West Seattle, White Center, Burien, Renton, Newcastle and Bellevue through Route 560.

[92] Prior to 2019, the Port of Seattle contracted out taxi services to an independent company, but changed to direct management with drivers due to protests over high access fees.