Katzenbach died Tuesday night of natural causes at his home in Princeton, N.J., according to his daughter, Anne Katzenbach of New York City.
The Supreme Court had declared racial segregation unconstitutional, but no federal law then required state universities to open their doors to all. When a black student named James Meredith obtained a court order to enroll at the University of Mississippi, Gov. Ross Barnett went on television to say he would "not surrender to the evil and illegal forces of tyranny."
Kennedy dispatched Katzenbach to Oxford, Miss., in September 1962 to enforce the court order. And with the help of 25,000 Army troops, Meredith was enrolled.
Katzenbach's confrontation with Wallace was one of the famous scenes of the civil rights era. Wallace had promised to stand in the schoolhouse door to preserve segregation.
Two black students, Vivian Malone and James Hood, had obtained court orders allowing them to enroll at the University of Alabama. A defiant Wallace placed himself in the doorway at Foster Auditorium on June 11, 1963, and proclaimed that "as governor of this sovereign state," he would not "willingly submit to illegal usurpation of power by the central government."
Katzenbach, tall and imposing, said he was not impressed with Wallace's "show." He told the governor he had a proclamation from the president of the United States ordering the students to be enrolled. And he had the backing of the Alabama National Guard, which had been federalized by Kennedy. At that, Wallace relented, and the students were admitted.
Five months later, on the day Kennedy was assassinated in Dallas, Lyndon Johnson called Katzenbach to consult on taking the presidential oath. Johnson was determined to be sworn in on Air Force One before returning to Washington.
Three days later, Katzenbach wrote a memo to the White House recommending a high-level government commission to investigate the assassination and put to rest the inevitable conspiracy theories. His advice led to the creation of the Warren Commission, led by the chief justice, but the memo was later cited by conspiracy buffs as the first sign of a cover-up.
After Robert Kennedy ran for a U.S. Senate seat in New York in 1964, Katzenbach became attorney general. And at Johnson's direction, he drafted what became the Civil Rights Act of 1964.
The act prohibited public schools and universities from discriminating based on race, and it required public businesses, including restaurant and hotels, to open their doors to all. Private employers were also prohibited from discriminating in hiring, firing and promotions.
Katzenbach also helped win passage of the Voting Rights Act of 1965, which put the force of the federal government behind ensuring that blacks could register and vote throughout the nation.
Katzenbach, however, could not win a fight within his own department to control the long-serving, imperious FBI director, J. Edgar Hoover, who insisted on wiretapping civil rights leader Martin Luther King Jr. Unable to rein in Hoover, Katzenbach stepped down in 1966 and moved to the State Department as undersecretary. His goal was to negotiate an end to the Vietnam War, but he left the government in 1969 with the war still raging.
Nicholas deBelleville Katzenbach was born Jan. 17, 1922, in Philadelphia and raised in New Jersey. He was 19 when he enlisted in the Army Air Corps. His B-25 bomber was shot down over the Mediterranean in 1943, and he spent two years as a prisoner of war in Italy and Germany.
After the war, he graduated from Princeton University and Yale Law School and studied two years in England on a Rhodes scholarship. He taught law at Yale and the University of Chicago before joining the government.
His 2008 memoir of his time in government was titled "Some of It Was Fun."
Besides his daughter Anne, Katzenbach is survived by his wife of 66 years, Lydia; another daughter, Maria Katzenbach of Portland, Ore.; sons Christopher of Mill Valley, Calif. and John of Amherst, Mass.; and six grandchildren.