Montgomery graduated from the University of Edinburgh with an arts degree. She submitted scripts to Associated British Picture Corporation where they attracted attention of Walter Mycroft who put her under contract.
Working for Gainsborough Pictures, her early credits include Just William (1940), The Man in Grey (1943), Fanny by Gaslight (1944) and While I Live (1947). Television credits include Dr. Finlay's Casebook and The Avengers (for which she created the character of Cathy Gale).
In 1954 he wrote the play A Summer House based on the Constance Kent murder cast. She also co wrote a book, Voices in the Dark (1971).
She died on 24 February 1992 in London.
- Mr. Reeder in Room 13 (1938)
- Lassie from Lancashire (1938)
- Meet Mr. Penny (1938)
- Dead Men Tell No Tales (1938)
- Poison Pen (1939)
- The Second Mr. Bush (1940)
- The House of the Arrow (1940)
- The Flying Squad (1940)
- At the Villa Rose (1940)
- Just William (1949)
- Bulldog Sees It Through (1940)
- The Man in Grey (1943)
- Fanny by Gaslight (1944)
- Love Story (1944)
- This Man Is Mine (1946)
- While I Live (1947)
- Shadow of the Eagle (1950)
- The Rival of the Empress (1951)
- The Scarlet Web (1954)
- Dance Little Lady (1954)
- Rheingold Theatre (1953–54) (TV series)
- Born for Trouble (1955) (TV series)
- The Narrowing Circle (1956)
- You Can't Escape (1956)
- Hawkeye and the Last of the Mohicans (1957) (TV series)
- William Tell (1958–59) - writer, story editor
- The New Adventures of Charlie Chan (1958) (TV series)
- Murder Reported (1958)
- H.G. Wells' The Invisible Man (1958) (TV series)
- Danger Man (1960) (TV series)
- Sir Francis Drake (1962) (TV series) - writer
- The Avengers (1963) (TV series)
- Crane (1964) (TV series) - writer "A Danger to Others"
- Dr. Finlay's Casebook (1964–65)(TV series) - various episodes
- No Hiding Place (1965) (TV series) - episode "A Fistful of Trouble"
- Who-Dun-It (1969) (TV series) - play basis for "Murder Goes to School"
- Avenger with a typewriter Cotes, Peter. The Guardian (1959-2003); London (UK) [London (UK)]09 Mar 1992: 37
- OBITUARIES Baker, Bob. Sight and Sound; London3.2 (Feb 1, 1993): 29.