William Ramsey Clark was born on December 18, 1927, in Dallas, Texas, the son of former attorney general and Supreme Court justice Tom C. Clark. He attended the University of Texas, receiving his B.A. in 1949, and then earned his M.A. in history and a law degree from the University of Chicago in 1950. He went on to practice law in Dallas.

In 1961, Clark was appointed U.S. assistant attorney general in charge of the Lands Division. He cut in half the backlog of thirty-two thousand pending cases while simultaneously cutting the staff and budget. After the court ordered the integration of the University of Mississippi in 1962, Clark led federal civilian forces there and then worked with other schools throughout the South, demonstrating his commitment to civil rights.

Clark was promoted to deputy attorney general on February 13, 1965. helping to draft the 1965 Voting Rights Act and coordinating forces sent to aid desegregation at the University of Alabama and the civil rights march from Selma to Montgomery.

When Nicholas Katzenbach resigned as head of the department on October 3, 1966, Clark became acting attorney general. He took over the justice department formally on February 28, 1967. His confirmation led his father to resign from the Supreme Court in order to avoid the suspicion of any conflict of interest. During his stint as attorney general, Clark was involved in drafting the administration's civil rights proposals and helped to ensure passage of the 1968 Civil Rights Act.

After the assassination of Martin Luther King Jr., Clark established a commission to study all government activities regarding Reverend King. He also made it a priority to fight organized crime. As a step in this fight, he initiated "strike forces," or groups composed of attorneys and workers from important government agencies that worked closely together to combat crime. Another Clark initiative was the combining of several government agencies into a centralized Bureau of Narcotics and Dangerous Drugs.

Clark was also a proponent of more gun-control legislation and of putting more importance on rehabilitation efforts in federal prisons. When the controversy over FBI eavesdropping arose, Clark initiated new guidelines restricting the use of wiretaps and electronic eavesdropping devices by federal agencies. In 1967, as a result of riots throughout the nation, Clark created the Interdivisional Information Unit as a part of the Justice Department.

When he left government service in January 1969, Clark joined a New York City law firm and became a loud opponent of the Vietnam War. Clark defended Reverend Philip F. Berrigan and five others indicted on charges of conspiring to kidnap Secretary of State Henry Kissinger and of blowing up heating systems in federal buildings throughout Washington D.C.Clark was also a part of a controversial investigative team that traveled to Hanoi to look into charges that America took aim at nonmilitary targets during its bombing raids over North Vietnam. In 1974, he won the Democratic primary for the U.S. Senate seat from New York, refusing to accept campaign contributions over $100. Despite winning the primary, Clark lost the general election.