President John F. Kennedy was assassinated by gunshot while traveling in a motorcade in an open-top limousine in Dallas, Texas at 12:30 pm CST on Friday, November 22, 1963; Texas Governor John Connally was wounded, but survived. Within two hours, Lee Harvey Oswald was arrested for killing Dallas policeman J. D. Tippit and arraigned that evening. Shortly after 1:30 am on Saturday, November 23, Oswald was arraigned for murdering President Kennedy as well. On Sunday, November 24, at 11:21 a.m., nightclub owner Jack Ruby fatally shot Oswald as he was being transferred from the city jail to the county jail.

Immediately after the shooting, many people suspected that the assassination was part of a larger plot, and broadcasters speculated that Dallas right-wingers were involved. Ruby's shooting of Oswald compounded initial suspicions. Among conspiracy theorists, author Mark Lane has been described as writing "the first literary shot" with his article, "Defense Brief for Oswald", in the National Guardian's December 19, 1963 issue. Thomas Buchanan's Who Killed Kennedy?, published in May 1964, has been credited as the first book to allege a conspiracy.

In 1964, the Warren Commission concluded that Oswald had acted alone and that no credible evidence supported the contention that he was involved in a conspiracy to assassinate the president. The Commission also indicated that then-Secretary of State Dean Rusk, then-Defense Secretary Robert S. McNamara, then-Treasury Secretary C. Douglas Dillon, then-Attorney General Robert F. Kennedy, then-FBI director J. Edgar Hoover, then-CIA director John A. McCone, and then-Secret Service Chief James J. Rowley, each individually reached the same conclusion on the basis of information available to them. During the trial of Clay Shaw in 1969, however, New Orleans District Attorney Jim Garrison challenged the single-bullet theory with evidence from the Zapruder film, which he claimed indicated that a fourth shot from the grassy knoll had caused the fatal shot to Kennedy's head.

In 1979, the United States House Select Committee on Assassinations (HSCA) agreed with the Warren Commission that Oswald did, in fact, assassinate Kennedy, but concluded that the Commission's report and the original FBI investigation were seriously flawed. The HSCA concluded that at least four shots were fired with a "high probability" that two gunmen fired at the President, and that a conspiracy to do so was probable. The HSCA stated that the Warren Commission had "failed to investigate adequately the possibility of a conspiracy to assassinate the President". The Ramsey Clark Panel and the Rockefeller Commission both supported the Warren Commission's conclusions.