Nicholas deBelleville Katzenbach was born on January 17, 1922, in Philadelphia, Pennsylvania. Katzenbach attended Princeton University, graduating in 1945, and he received his law degree from Yale Law School in 1947. Katzenbach also received a Rhodes scholarship and studied at Oxford University for two years.

Returning to the United States, Katzenbach accepted teaching positions first at Yale and then the University of Chicago Law School. He continued teaching until 1960. In 1961, he was appointed assistant attorney general in charge of the justice department's Office of Legal Counsel. In April 1962, he was promoted to deputy attorney general, the second highest position in the department. Katzenbach would be involved in the drafting of the Communications Satellite Act of 1962 and the Kennedy administration's foreign trade program.

He was also involved in securing the release of prisoners captured during the Bay of Pigs raid on Cuba. Katzenbach took an active role in the Justice Department's fight for civil rights, overseeing departmental operations in desegregating the University of Mississippi in September 1962 and the University of Alabama in June 1963. He also worked with Congress to ensure the passage of the 1964 Civil Rights Act.

Katzenbach, at Robert Kennedy's suggestion, was named attorney general on January 28, 1965. In April 1965, after knowledge of a wiretap on Martin Luther King was made public, Katzenbach ordered an end to the tap and continued his support for civil rights. He acquired a federal court order prohibiting state officials from interfering with the Selma to Montgomery civil rights marchers and drafted the voting rights bill proposed by the Johnson administration.

Katzenbach worked to enforce the bill and defend its constitutionality before the Supreme Court in January 1966. He then played an integral role in the drafting of the Johnson administration's civil rights bill in 1966, as well as the administration's anticrime proposal in March of the same year. In July 1965, he was chosen to head the presidential Commission on Law Enforcement and the Administration of Justice. He ran into difficulties, however, with FBI director J. Edgar Hoover over a mail-opening operation and unauthorized wiretaps of Martin Luther King's hotel rooms.

Katzenbach resigned in 1966, stating "he could no longer effectively serve as attorney general because of Mr. Hoover's obvious resentment of me." President Johnson then appointed him undersecretary of state on September 21, 1966. In that capacity, Katzenbach went on fact-finding missions to South Vietnam in 1966 and 1967. He also headed diplomatic trips in Africa, India, and Western and Eastern Europe.

Johnson also appointed Katzenbach to a three-member commission charged with reviewing CIA activities, including the agency's questionable use of funds. Following the commission's report, President Johnson prohibited the use of covert government aid for private educational, philanthropic, and cultural organizations. Katzenbach resigned as undersecretary in November 1968 but agreed to stay on in the State Department during the transfer of power following Nixon's election. In 1969, Katzenbach became vice president and general counsel of International Business Machines Corporation.