Millar's books are distinguished by sophistication of characterization. Often we are shown the rather complex interior lives of the people in her books, with issues of class, insecurity, failed ambitions, loneliness or existential isolation or paranoia often being explored with an almost literary quality that transcends the mystery genre. Unusual people, mild societal misfits or people who don't quite fit into their surroundings are given much interior detail. In some of the books (for example in The Iron Gates) we are given chilling and fascinating insight into what it feels like to be losing touch with reality and evolving into madness. In general, she is a writer of both expressive description and yet admirable economy, often ambitious in the sociological underpinnings of the stories and the quality of the writing.

Millar often delivers effective and ingenious "surprise endings," but the details that would allow the solution of the surprise have usually been subtly included, in the best genre tradition. One of the distinctions of her books, however, is that they would be interesting, even if you knew how they were going to end, because they are every bit as much about subtleties of human interaction and rich psychological detail of individual characters as they are about the plot.

Millar was a pioneer in writing intelligently about the psychology of women. Even as early as the '40s and '50s, her books have a very mature and matter-of-fact view of class distinctions, sexual freedom and frustration, and the ambivalence of moral codes depending on a character's economic circumstances. Her earliest novels seem unusually frank. Read against the backdrop of Production Code-era movies of the time, they remind us that life as lived in the '40s and '50s was not as black-and-white morally as Hollywood would have us believe.

Many websites cite her as working as a screenwriter for Warner Brothers just after World War II, but no further details are given as to what she may have worked on, even on imdb.com. Around that time, Warners bought the option on her novel The Iron Gates, with its chilling portrait of a woman descending into madness, but reportedly Bette Davis and other prominent Warner Brothers actresses ultimately turned it down because the memorable protagonist is missing for the last third of the story. The film was never produced. In the early '60s, two of her novels (Beast in View and Rose's Last Summer) were adapted for the anthology TV series Alfred Hitchcock Presents and Thriller.

While she was not known for any one recurring detective (unlike her husband, whose constant gumshoe was Lew Archer), she occasionally used a detective character for more than one novel. Among her occasional ongoing sleuths were Canadians Dr. Paul Prye (her first invention, in the earliest books) and Inspector Sands (a quiet, unassuming Canadian police inspector who might be the most endearing of her recurring inventions). In the California years, a few books featured either Joe Quinn, a rather down-on-his-luck private eye, or Tom Aragorn, a young, Hispanic lawyer.

Sadly, most of Millar's books are out of print in America, with the exception of the short story collection The Couple Next Door and two novels, "An Air That Kills" and "Do Evil In Return", that have been re-issued as classics by Stark House Press in California.

In 1956 Millar won the Edgar Allan Poe Awards, Best Novel award for Beast in View. In 1965 she was awarded the Woman of the Year Award by the Los Angeles Times.

In 1983 she was awarded the Grand Master Award by the Mystery Writers of America in recognition of her lifetime achievements.

In 1987, critic and mystery writer H.R.F Keating included Millar's Beast In View in his Crime & Mystery: The 100 Best Books. He wrote:

"Margaret Millar is surely one of late twentieth-century crime fiction's best writers, in the sense that the actual writing in her books, the prose, is of superb quality. On almost every page of this one there is some description, whether of a physical thing or a mental state, that sends a sharp ray of extra meaning into the reader's mind."

One of S.J. Perelman's classic, comic feuilletons (as he styled them), titled Oh, I Am a Cook and a Houseboy Bland was inspired by a columnist's item about the Millars, in which they described their daily writing routine, taking place in separate wings of their house:

'I'm a morning person,' says Mrs Millar, 'He's an afternoon person.''We occasionally meet on the stairs,' says Mr Millar.

Perelman's sardonic piece, told from the point of view of their 'Annamite houseman', portrayed a pair of vainglorious and mutually suspicious hacks.

"Paul Prye" Mystery Novels

• The Invisible Worm (1941)
• The Weak-Eyed Bat (1942)
• The Devil Loves Me (1942)

"Inspector Sands" Mystery Novels

• Wall of Eyes (1943)
• The Iron Gates [Taste of Fears] (1945)

"Tom Aragon" Mystery Novels

• Ask for Me Tomorrow (1976)
• The Murder of Miranda (1979)
• Mermaid (1982)

Other Mystery Novels

• Fire Will Freeze (1944)
• Do Evil in Return (1950)
• Rose's Last Summer (1952)
• Vanish in an Instant (1952)
• Beast in View (1955) (Edgar Award for Best Novel, 1956)
• An Air That Kills [The Soft Talkers] (1957)
• The Listening Walls (1959)
• A Stranger in My Grave (1960)
• How Like an Angel (1962)
• The Fiend (1964)
• Beyond This Point Are Monsters (1970)
• Banshee (1983)
• Spider Webs (1986)
• The Couple Next Door: Collected Short Mysteries. Ed. Tom Nolan (2004)

Other Novels

• Experiment in Springtime (1947)
• It’s All in the Family (1948)
• The Cannibal Heart (1949)
• Wives and Lovers (1954)
• The Birds and the Beasts Were There (1968) (memoir)

Theme issue on Margaret Millar. Guest ed. Dean James. CLUES: A Journal of Detection 25.3 (Spring 2007). She features largely in Tom Nolan's biography of her husband, Ross Macdonald (New York: Scribner, 1999). ISBN 0-684-81217-7)