Although the assassination of President John F. Kennedy in 1963 did not lead to any very immediate gun control laws, it did help to create more demand for gun control and more public attention to the issue. This attention eventually led to the Gun Control Act of 1968.
In 1963, Senator Thomas Dodd of Connecticut was sponsoring a bill to curtail the availability of handguns via mail-order. When President Kennedy was assassinated, Dodd added rifles to his bill because Lee Harvey Oswald had obtained the rifle he used to kill the President through the mails. However, this bill never made it out of committee.
No gun control law actually managed to pass Congress until 1968. By then, support for the law had increased because of (among other things) the assassinations of President Kennedy's brother Robert and of Martin Luther King, Jr. Thus, we can say that JFK's assassination helped to create an impetus for gun control, though we must recognize that other events had to happen to create enough of a push to get a gun control law through Congress.