Kennedy Onassis was the main organizer of her husband's state funeral, which was inspired from Abraham Lincoln's funeral. She wanted her husband's casket to be closed, even though her brother-in-law and Attorney General, Robert F. Kennedy wanted it to be open. The funeral service was held at the Cathedral of St. Matthew the Apostle in Washington D.C., with the burial taking place at nearby Arlington National Cemetery. Many admired her role and appearance at the funeral. The "Evening Standard" wrote "Jacqueline Kennedy has given the American people ... one thing they have always lacked: Majesty".
A week after the assassination, President Lyndon B. Johnson issued an executive order that created the Warren Commission—led by Chief Justice Earl Warren—to investigate the assassination. Ten months later, the Commission issued its report finding that Lee Harvey Oswald had acted alone when he assassinated President Kennedy. Kennedy Onassis did not care about the investigation. She said that even if they had the right suspect, it would not bring her husband back. She gave her testimony to the commission detailing the events of her husband's assassination.
After the assassination, Kennedy Onassis and her children stepped back from public view and activities.
On November 29, 1963, a week after her husband's assassination, Theodore H. White of "Life" magazine interviewed Kennedy Onassis at her home in Hyannis Port. While being interviewed, she compared the Kennedy years in the White House to King Arthur's Camelot. Kennedy Onassis said that the her husband played the title song of Lerner and Loewe's musical recording before going to bed. She quoted a line from the musical, trying to show how the loss felt by saying "Don't let it be forgot, that once there was a spot, for one brief, shining moment that was known as Camelot. There'll be great presidents again ... but there will never be another Camelot". As a result, her husband was nicknamed "Camelot" and his presidency the "Camelot Era".
Kennedy Onassis and her children stayed in the White House for two weeks after the assassination. President Lyndon B. Johnson wanted to "do something nice for Jackie", President Johnson wanted to make her Ambassador to France, but she turned the offer down, as well as other offers of ambassadorships to Mexico and the United Kingdom. Johnson renamed the Florida space center the John F. Kennedy Space Center a week after the assassination. Kennedy Onassis later publicly thanked Johnson for his kindness to her.
Kennedy Onassis spent 1964 in mourning and made few public appearances. Some believed she was suffering from post traumatic stress disorder. In the winter after the assassination, she and the children stayed at Averell Harriman's home in Georgetown. On January 14, 1964, she made a televised appearance from the office of the Attorney General, thanking the public for the "hundreds of thousands of messages" she had received since the assassination. She bought a house for herself and her children in Georgetown, but sold it later in 1964. She bought a 15th-floor penthouse apartment for $250,000 at 1040 Fifth Avenue in Manhattan to have more privacy.
Kennedy Onassis would go to a few memorial ceremonies dedicated to her late husband. In 1967, she attended the christening of the U.S. Navy aircraft carrier . She also went to a private ceremony in Arlington National Cemetery that saw the moving of her husband's coffin, after which he was buried again so that officials at the cemetery could build a safer eternal flame. She also was in charge of the creation of the John F. Kennedy Presidential Library and Museum.
During the Vietnam War in November 1967, "Life" magazine named Kennedy Onassis "America's unofficial roving ambassador" when she and David Ormsby-Gore, former British ambassador to the United States, traveled to Cambodia. Many historians saw that her visit was "the start of the repair to Cambodian-US relations, which had been at a very low ebb". She also went to the funeral services of Martin Luther King Jr. in Atlanta, Georgia, in April 1968.
After her husband's assassination, Kennedy Onassis became closer with her brother-in-law Robert F. Kennedy. After President Kennedy's assassination, Robert became a father figure for her children. Kennedy Onassis supported him staying in politics, and she supported his 1964 campaign for United States senator from New York.
When President Johnson's approval ratings fell, many wanted Senator Kennedy to run for president in 1968. When Art Buchwald asked him if he wanted to run, Robert replied, "That depends on what Jackie wants me to do". She met with him around this time and she told him to run, however she was worried about his safety.
Just after midnight PDT on June 5, 1968, a Palestinian gunman named Sirhan Sirhan shot Senator Kennedy minutes after he and a crowd of his supporters had been celebrating his victory in the California Democratic presidential primary. Kennedy Onassis went to Los Angeles to be with Senator Kennedy's wife Ethel, her brother-in-law Ted, and the other Kennedy family members at his hospital bedside. Robert Kennedy died the next day, aged 42.
After Robert Kennedy's death in 1968, Kennedy Onassis suffered from depression again. She became worried about her life and those of her two children, saying: "If they're killing Kennedys, then my children are targets ... I want to get out of this country".
On October 20, 1968, Kennedy Onassis married her long-time friend Aristotle Onassis, a wealthy Greek businessman who was able to give the privacy and security she wanted for herself and her children. The wedding took place on Skorpios, Onassis's private Greek island in the Ionian Sea. After marrying Onassis, she took the legal name Jacqueline Onassis and lost her right to Secret Service protection. The fact that Aristotle was divorced and his former wife Athina Livanos was still living, many believed that Jacqueline might be excommunicated by the Roman Catholic church. She was seen by some as a "public sinner".
During their marriage, the Onassiss had six different homes: her 15-room Fifth Avenue apartment in Manhattan, her horse farm in New Jersey, his Avenue Foch apartment in Paris, his private island Skorpios, his house in Athens, and his yacht "Christina O".
Aristotle Onassis's health became worse after the death of his son Alexander in a plane crash in 1973. Aeristotle Onassis died of respiratory failure caused by myasthenia gravis at aged 69 in Paris on March 15, 1975. After two years of legal wrangling, Kennedy Onassis accepted a settlement of $26 million from Christina Onassis, Aristotle's daughter.
After the death of her second husband, Kennedy Onassis returned to the United States, spending her time between Manhattan, Martha's Vineyard, and the Kennedy Compound in Hyannis Port. In 1975, she became an editor at Viking Press, a position that she held for two years.
After almost ten years without going to a political event, Kennedy Onassis went to the 1976 Democratic National Convention. She resigned from Viking Press in 1977 after John Leonard of "The New York Times" said that she had some responsibility for Viking's publication of the Jeffrey Archer novel "Shall We Tell the President?". The novel is set in a fictional future presidency of Ted Kennedy and talked about an assassination plot against him. Two years later, she appeared alongside her mother-in-law Rose Kennedy in Boston when Ted Kennedy announced that he was going to run against President Jimmy Carter for the Democratic nomination for president.
After she left Viking Press, Kennedy Onassis was hired by Doubleday, where she worked as an associate editor. Some of the books she edited for the company were Larry Gonick's "The Cartoon History of the Universe", the English translation of the three volumes of Naghib Mahfuz's "Cairo Trilogy", and autobiographies of ballerina Gelsey Kirkland, singer-songwriter Carly Simon, and fashion icon Diana Vreeland.