Born in Los Angeles, Margaret was the younger sister of actor Elmer Booth, who starred in several films for D. W. Griffith.

She later joined Louis B. Mayer's namesake studio, where she was mentored by film director John M. Stahl.

After Thalberg's death, Mayer appointed Booth as the studio's supervising film editor, a position she held for nearly three decades.

In 1968, Booth retired from MGM, and was hired by Ray Stark as a supervising film editor for his studio Rastar Productions.

[2] At Elmer's funeral, Griffith delivered an eulogy and approached Margaret with a job offer as a film joiner (also known as a negative cutter) to provide income for the family.

After a few months, Booth worked for Paramount Pictures' editing department, assembling the tinted sections for release prints.

After he left, Booth took her own approach; when Stahl screened her work, he was impressed and hired her immediately as his editorial assistant.

Stahl stayed with MGM for several years,[11] but when he left the studio in 1927, he asked Booth to join him but she declined.

[16][17] In his 1995 book Making Movies, director Sidney Lumet called Booth "a remarkable person.

"[18] He told one story while filming The Hill (1965) in England, in which she arrived on location and asked to see a rough-cut version, promptly at eight during the following morning.

Following the third screening, Lumet consoled a despondent Booth, who personally felt none of the new studio executives knew or care about filmmaking.

[16][20] In its 1982 article about Booth's long tenureship, the Village Voice describes her as "the final authority of every picture the studio made for 30 years.

"[21] After leaving MGM, Booth was hired by Ray Stark as the supervising editor for his company, Rastar Productions.

She supervised the editing for several films, including The Way We Were (1973), The Sunshine Boys (1975), The Goodbye Girl (1977), California Suite (1978), and Annie (1982).

[22] On her centennial birthday, in 1998, Booth was honored with a gala commemorating her seven-decade contributions to the film industry at the Sheraton Universal Hotel, hosted by the Motion Picture Editors Guild.

[13] In their obituary for Booth, the British newspaper The Guardian stated, "All the filmmakers had to go through her in order to have a final editing of sound and vision approved," while describing her approach:She was a pioneer of the classic editing style, the so-called "invisible cutting", the aim of which was to make the transition from one image to another as seamless as possible, so the audience was almost unaware of the flow of shots within a sequence.