Clairton's existence dates to just after the turn of the 20th century, when the Crucible Steel Company acquired a large tract along the west side of the Monongahela River, approximately 13 miles (21 km) south of Pittsburgh. Soon after, the Carnegie Steel Company (later U.S. Steel) built an integrated steel mill and coke production facility, which eventually became one of the world's largest.

The site had more than 1,000 acres (4.0 km²) of level land suitable for a large industrial complex. On April 12, 1903, Clairton was incorporated as a borough, and on January 1, 1922, Clairton was incorporated as a City of the Third Class with a population of approximately 11,000. This incorporation was prompted by industry, which was taxed by the three boroughs - Clairton, Wilson and North Clairton - which were chartered separately prior to the incorporation of the City of Clairton.

During the next several decades, growth and advancement indicated a thriving city. As the steel mill and coke production facilities expanded, the population of Clairton grew. Clairton took on a life of its own, including a business district and educational, religious, and cultural facilities. The city peaked in the late 1950s, and has been in decline since.

In the late 1950s, Clairton High School (CHS) had a large student body, and the city had a "feeder" system of public and parochial elementary schools. The CHS student body was soon siphoned off, however, by new schools in Elizabeth Borough, Snowden Township, and Jefferson Borough. During the mid-1950s and into the 1960s, CHS was a Class AAA competitor in the formidable Western Pennsylvania Interscholastic Athletic League (WPIAL), playing against high schools in other mill towns up and down the Monongahela River Valley.

With the decline of the steel industry in the 1980s, Clairton began to experience severe problems in its employment and tax base, which spurred a major economic shock to the community. In 1988, Clairton was designated a distressed municipality by Pennsylvania's Department of Community Affairs (DCA). Pursuant to Act 47 of 1987 (the Financially Distressed Municipalities Act), DCA commissioned the development of a recovery plan for Clairton. By 1988, the Clairton School District had consolidated its entire system into a single building (a remodeled version of the high school) and closed its other schools. Clairton High now competes at the Class A level in the WPIAL. The high school football team has had national prominence for recent success.

Clairton is located along the Monongahela River and is part of the Pittsburgh metropolitan area. The population was 6,181 at the 2020 census. Under Pennsylvania legal classifications for local governments, Clairton is considered a third-class city. It is home to Clairton Works operated by U.S. Steel, the largest coke manufacturing facility in the United States.