She died from metastatic cancer at her home in Rancho Mirage, California, on Wednesday surrounded by loved ones, according to her family.
"Marcia was a force," her family said in a statement to US media on Friday. "A true trailblazer for women in film and one of the most influential editors in cinematic history; she helped redefine what film editing could be."
Lucas won the Academy Award for Best Film Editing for 1977's Star Wars - later renamed A New Hope - alongside editors Richard Chew and Paul Hirsch.
Although her contributions largely took place behind the scenes, her role in shaping the film's emotional heart and narrative structure has been widely recognised in the decades since its release.
George Lucas credited her with helping make sense of the vast amount of footage filmed for the climactic Death Star battle sequence.
"It was extremely complex and we had 40,000 feet of dialogue footage of pilots saying this and that," he told Rolling Stone shortly after the film's release.
"Nobody really has ever tried to interweave an actual plot story into a dogfight, and we were trying to do that."
Born Marcia Griffin in Modesto, California, in 1945, she began her career as a film librarian before becoming one of Hollywood's most respected editors.
