Clark, the son of U.S. Supreme Court Justice Tom Clark, practiced law in Dallas early in his career and became a federal assistant attorney general in 1961.
When courts ordered the integration of the University of Mississippi in 1962, Clark led civilian federal workers there, and went on to work on other civil rights cases in the South.
Clark was the federal official responsible for protecting marchers in the 1965 march in Alabama from Selma to Montgomery. The first night of the march, “I felt like we were in the Civil War,” Clark told an interviewer.
After he left the government in 1969, Clark practiced and taught law in Manhattan, and loudly opposed the Vietnam War.
He ran unsuccessfully in 1974 for the New York U.S. Senate seat held by liberal Republican Jacob Javits, and gained attention for limiting campaign contributions at $100. Javits defeated him by seven percentage points.