Kopechne was born in Wilkes-Barre, Pennsylvania, and was the daughter and only child of Joseph and Gwen Kopechne. Her father worked as a insurance salesman. Kopechne was of Polish-American heritage. Her family moved to Berkeley Heights, New Jersey when Kopechne was an infant. She attended parochial schools growing up. After graduating with a degree in business administration from Caldwell College for Womenin 1962, Kopechne moved to Montgomery, Alabama, to teach for a year at the Mission of St. Jude, an activity that was part of the Civil Rights Movement. By 1963, Kopechne relocated to Washington, D.C., to work as secretary for Florida Senator George Smathers. She joined New YorkSenator Robert F. Kennedy's secretarial staff following his election in November 1964. For that office she worked as a secretary to the senator's speechwriters and as a legal secretary to one of his legal advisers. Kopechne was a loyal worker. Once, during March 1967, she stayed up all night at Kennedy's Hickory Hill home to type a major speech against the Vietnam War, while the senator and his aides such as Ted Sorenson made last-minute changes to it.
During the 1968 U.S. presidential election, Kopechne helped with the wording of Kennedy's speech of March 1968 announcing his presidential candidacy. During his campaign, she worked as one of the "Boiler Room Girls". This was an affectionate nickname given to six young women whose office area was in a hot, loud, windowless location in Kennedy's Washington campaign headquarters. They were vital in tracking and compiling data and intelligence on how Democratic delegates from various states were intending to vote; Kopechne's responsibilities includedPennsylvania. Kopechne and the other staffers were knowledgeable politically, and were chosen for their ability to work skillfully for long, hectic hours on sensitive matters. They talked daily with field managers and also helped distribute policy statements to strategic newspapers.
Kopechne was devastated emotionally by the assassination of Robert F. Kennedy on June 5, 1968. After working briefly for the Kennedy proxy campaign of George McGovern, she stated she could not return to work on Capitol Hill, saying "I just feel Bobby's presence everywhere. I can't go back because it will never be the same again." But as her father later said, "Politics was her life," and in December 1968 she used her experience to gain a job with Matt Reese Associates, a Washington, D.C., firm that helped establish campaign headquarters and field offices for politicians and was one of the first political consulting companies. By mid-1969 she had completed work for a mayoral campaign in Jersey City, New Jersey. She was on her way to a successful professional career. Kopechne lived in the Washington neighborhood of Georgetown with three other women. She was a fan of theBoston Red Sox and of fellow Polish-American Carl Yastrzemski. She was a devout Roman Catholic with a demure, serious, "convent school" demeanor, rarely drank much, and had no reputation for extramarital activities with men.
On July 18, 1969, Kopechne attended a party on Chappaquiddick Island, off the coast of Martha's Vineyard, Massachusetts. The celebration was in honor of the dedicated work of the Boiler Room Girls, and was the fourth such reunion of the Robert F. Kennedy campaign workers. Kopechne reportedly left the party at 11:15 p.m. with Robert's brother Ted, after he — according to his own account — offered to drive her to catch the last ferry back to Edgartown, where she was staying. She did not tell her close friends at the party that she was leaving, and she left her purse and keys behind. Kennedy drove the 1967 Oldsmobile Delmont 88 off a narrow, unlit bridge, which was without guardrails and was not on the route to Edgartown. The Oldsmobile landed in Poucha Pond and overturned in the water; Kennedy extricated himself from the vehicle and survived, but Kopechne did not.
Kennedy failed to report the incident to the authorities until the car and Kopechne's body were discovered the next morning. Kopechne's parents said that they learned of their daughter's death from Kennedy himself, before he informed authorities of his involvement. However, they learned Kennedy had been the driver from wire press releases some time later. A private funeral for Kopechne was held on July 22, 1969, at St. Vincent's Roman Catholic Church in Plymouth, Pennsylvania, attended by Kennedy. She is buried in the parish cemetery on the side of Larksville Mountain.
A week after the incident, Kennedy pleaded guilty to leaving the scene of an accident after causing injury. He received a two-month suspended sentence. On a national television broadcast that night, Kennedy said that he had not been driving "under the influence of liquor" nor had he ever had a "private relationship" with Kopechne. The Chappaquiddick incident and Kopechne's death became the topic of at least 15 books, as well as a fictionalized treatment by Joyce Carol Oates. Questions remained about Kennedy's timeline of events that night, specifically his actions following the incident. The quality of the investigation has been scrutinized, particularly whether official deference was given to a powerful and influential politician, and his family. The events surrounding Kopechne's death damaged Kennedy's reputation and are regarded as a major reason that he was never able to mount a successful campaign for President of the United States.Kennedy expressed remorse over his role in her death, in his posthumously-published memoir, True Compass