President Gerald Ford appointed William Thaddeus Coleman, Jr., to serve as the nation's fourth secretary of the Department of Transportation on March 7, 1975, replacing Claude Brinegar, who had resigned. Coleman was born in Philadelphia, Pennsylvania, in 1920, and attended local public schools. He graduated summa cum laude from the University of Pennsylvania in 1941 and magna cum laude from Harvard Law School in 1946.

He began his legal career in 1947, serving as law clerk to Judge Herbert F. Goodrich of the Court of Appeals for the Third Circuit and clerk to Supreme Court Justice Felix Frankfurter in 1948. Coleman was one of the lead strategists and coauthor of the legal brief in Brown v. Board of Education (1954) in which the Supreme Court outlawed segregation in public schools.

He served as a member of the NAACP's national legal committee, director and member of its executive committee, and president of the NAACP Legal Defense and Educational Fund. Coleman was also a member of President Dwight Eisenhower's Committee on Government Employment Policy (1959-1961), a senior consultant and assistant counsel to the President's Commission on the Assassination of President John F. Kennedy (1964), and a consultant to the U.S. Arms Control and Disarmament Agency (1963-1975).In 1969, he was a member of the U.S. delegation to the twenty-fourth session of the United Nations General Assembly. Coleman was also a member of the National Commission on Productivity from 1971 to 1972. He was senior partner in the law firm of Dilworth, Paxson, Kalish, Levy & Coleman at the time of his appointment to the Ford administration.

When President Ford appointed him as secretary of Transportation, Coleman became only the second African American to serve in a cabinet post. At Transportation, Coleman was the point man for the administration's changes to the regulations governing the transportation industry. His most controversial decision was in allowing limited transatlantic service for the supersonic transport plant, the Concorde, a decision which angered the majority of environmental groups concerned largely with the effects of noise pollution. Close on the heels of the Concorde decision in terms of controversy was Coleman's decision to defer the mandatory installation of airbags in all new automobiles.

At the end of the Ford administration, Coleman returned to practicing law.