Her family history in the Wyoming Valley area of northeastern Pennsylvania traces back 250 years on her maternal side.

[12] After graduation, Kopechne moved to Montgomery, Alabama, for a year at the Mission of St. Jude,[3] which participated in the Civil Rights Movement.

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 Sorensen made last-minute changes to it.

[7][9][15][18] They were vital in tracking and compiling data and intelligence on how Democratic delegates from various states were intending to vote; Kopechne's responsibilities included Pennsylvania.

[15][18] Kopechne and the other staffers were knowledgeable politically,[18] and were chosen for their ability to work skillfully for long, hectic hours on sensitive matters.

[15] In September 1968, she was hired by Matt Reese Associates,[20] a Washington, D.C., firm that helped establish campaign headquarters and field offices for politicians, and was one of the first political consulting companies.

[13][21] In the fall elections of 1968, Kopechne did work on the re-election campaign of Senator Joseph S. Clark, Jr. (D-PA), who eventually lost.

The celebration was in honor of the dedicated work of the Boiler Room Girls, and was the fourth such reunion of Robert Kennedy campaign workers.

[17] Kopechne reportedly left the party with Kennedy at 11:15 p.m.; according to his account, he had offered to drive her to catch the last ferry back to Edgartown, where she was staying.

[5] The exact time and cause of Kopechne's death is not positively known, due to conflicting witness testimony at the January 1970 inquest, and lack of an autopsy.

[27] Massachusetts officials pressed for weeks to have Kopechne's body exhumed for an autopsy,[28] but in December 1969, a Pennsylvania judge sided with the parents' request not to disturb her burial site.

[29] Even otherwise sympathetic, mainstream biographers believed there were outstanding serious questions about Kennedy's timeline of events that night, specifically his actions following the incident.

[30] The events surrounding Kopechne's death damaged Kennedy's reputation, and are regarded as a major reason why he was never able to mount a successful campaign for President of the United States and essentially chose not to pursue the office.

[31] Kennedy would eventually overcome this and some lesser personal scandals to have a very long career as a Senator and to achieve a lengthy list of major legislative accomplishments.

[32] But the disparity of the outcomes remained; Kennedy biographer Peter Canellos has written of the aftermath: "Every day that he lived was one that Kopechne – a talented woman with political interests of her own – would not.

[4] In 2015, two cousins of Kopechne's in Pennsylvania self-published the book Our Mary Jo, which sought to emphasize the influence of her life, rather than discuss Kennedy or Chappaquiddick.

[34] A full biography, Before Chappaquiddick: The Untold Story of Mary Jo Kopechne (2020), was written by William C. Kashatus and published by Potomac Books.