Screenwriter and producer. UK-born Miss Harrison became the first female screenwriter to be nominated for the Best Original Screenplay Oscar when the category was introduced in 1940, and was the first screenwriter to received two Academy Award nominations in the same year in separate categories, for co-writing the screenplay for the films Foreign Correspondent (1940) (original) and Rebecca (1940) (adapted), both directed by Alfred Hitchcock, with whom she had a long professional relationship.
In 1933, she became Alfred Hitchcock's secretary after answering a newspaper advertisement. She began reading books and scripts for him and became one of Hitchcock's most trusted associates. Harrison appears in a scene in Hitchcock's original version of The Man Who Knew Too Much (1934), eating dinner with Peter Lorre's character. Hitchcock developed the habit of taking Harrison to dinner and recounting the details of hundreds of murders; Harrison had developed an interest in criminology. She worked with Hitchcock on other areas of his film's production to his wife Alma Reville. The couple became close to Harrison. She was among the screenwriters for Hitchcock film Jamaica Inn (1939) based on the novel by Daphne du Maurier, her first script.
When Hitchcock moved to Hollywood in March 1939 to begin his contract with David O. Selznick to direct films, Harrison emigrated with him as an assistant and writer. She continued contributing to the screenplays for Hitchcock's films Rebecca (1940), another du Maurier adaptation, Foreign Correspondent (1940), Suspicion (1941), and Saboteur (1942).
Harrison worked in television with Hitchcock together when she produced his TV series Alfred Hitchcock Presents (with Norman Lloyd) and Suspicion. From 1955 to 1962, she produced the TV series, Alfred Hitchcock Presents (1955).
Harrison married thriller novelist Eric Ambler in 1958; the couple remained married until her death in 1994. She and Ambler lived in London for the last 20 years of her life.