Mitchell was born in Detroit, Michigan, and grew up on Long Island in New York. He earned his law degree from Fordham University and was admitted to the New York bar in 1938. Except for three years' service in the navy, from 1938 until 1960 Mitchell practiced law in New York City.
Richard Nixon met John Mitchell when his law firm merged with Mitchell's in 1967. The two men became friends, and in 1968, with considerable trepidation, Mitchell agreed to become Nixon's presidential campaign manager.
During his successful 1968 campaign, Nixon turned over the details of the day-to-day operations to the superbly organized Mitchell. After he became president in January 1969, Nixon appointed Mitchell attorney general. Mitchell remained in office from 1969 until he resigned in 1972 to manage President Nixon's successful reelection campaign. As attorney general, Mitchell believed that the government's need for "law and order" justified restrictions on civil liberties. He advocated the use of wiretaps in national security cases without obtaining a court order and the right of police to employ the preventive detention of criminal suspects. He brought conspiracy charges against critics of the Vietnam War, and demonstrated a reluctance to involve the Justice Department in civil rights issues. "The Department of Justice is a law enforcement agency," he told reporters. "It is not the place to carry on a program aimed at curing the ills of society."
On February 21, 1975 Mitchell was found guilty of conspiracy, obstruction of justice, and perjury and sentenced to two and a half to eight years in prison for his role in the Watergate break-in and cover-up. Tape recordings made by President Nixon and the testimony of others involved confirmed that Mitchell had participated in meetings to plan the break-in of the Democratic party's national headquarters in the Watergate complex. In addition, he had met, on at least three occasions, with the president in an effort to cover up White House involvement after the burglars were discovered and arrested. He died after collapsing in front of his Washington, DC home in 1988. His wife Martha passed away in 1976.