Ngaio () Marsh was educated at St Margaret's College in Christchurch, New Zealand, where she was a foundation pupil. She studied painting at the Canterbury College School of Art before becoming an actress with the Allan Wilkie company touring New Zealand. From 1928 onward she divided her time between living in the United Kingdom and in her native New Zealand. She was made a Dame Commander of the British Empire in 1966.

Internationally she is best known for her 32 detective novels published between 1934 and 1982. Along with Dorothy L. Sayers, Margery Allingham and Agatha Christie, she has been classed as one of the four original "Queens of Crime"—female British crime writers who dominated the crime fiction genre in the Golden Age of the 1920s and 1930s.

All her novels feature British CID detective Roderick Alleyn. Several novels feature Marsh's other loves, the theatre and painting. A number are set around theatrical productions (Enter a Murderer, Vintage Murder, Overture to Death, Opening Night, Death at the Dolphin, and Light Thickens), and two others about actors off stage (Final Curtain and False Scent). Her short story "'I Can Find My Way Out" is also set around a theatrical production and is the earlier "Jupiter case" referred to in Opening Night. Alleyn marries a painter, Agatha Troy, whom he meets during an investigation (Artists in Crime), and who features in several later novels.

Most of the novels are set in England, but four are set in New Zealand, with Alleyn either on secondment to the New Zealand police (Vintage Murder, Colour Scheme, and Died in the Wool), or on holiday (Photo Finish); Surfeit of Lampreys begins in New Zealand but continues in London.

Marsh's great passion was the theatre. In 1942 she produced a modern-dress Hamlet for the Canterbury University College Drama Society (now UCDS), the first of many Shakespearean productions with the society until 1969. In 1944, Hamlet and a production of Othello toured a theatre-starved New Zealand to rapturous acclaim. In 1949, assisted by entrepreneur Dan O'Connor, her student players toured Australia with a new version of Othello and Pirandello's Six Characters in Search of an Author. In the 1950s she was involved with the New Zealand Players, a relatively short-lived attempt at a national professional touring repertory company.

She lived long enough to see New Zealand with a viable professional theatre industry with realistic Arts Council support, with many of her protégés to the forefront. The 430-seat Ngaio Marsh Theatre at the University of Canterbury is named in her honour. Her home on the Cashmere Hills is preserved as a museum.

She never married or had any children. Ngaio Marsh published a lyrical but not very revealing autobiography, Black Beech & Honeydew (Collins) in 1965. British author and publisher Margaret Lewis wrote an authorized biography, Ngaio Marsh, A Life (Chatto and Windus, ISBN 0-908912-06-4) in 1991. New Zealand art historian Joanne Drayton's biography, Ngaio Marsh: Her Life in Crime was published by HarperCollins in 2008.

Detective Novels

• A Man Lay Dead (1934)
• Enter a Murderer (1935)
• The Nursing Home Murder (1935)
• Death in Ecstasy (1936)
• Vintage Murder (1937)
• Artists in Crime (1938)
• Death in a White Tie (1938)
• Overture to Death (1939)
• Death at the Bar (1940)
• Surfeit of Lampreys (1941), published in USA as Death of a Peer
• Death and the Dancing Footman (1942)
• Colour Scheme (1943)
• Died in the Wool (1945)
• Final Curtain (1947)
• Swing Brother Swing (1949), published in USA as A Wreath for Rivera
• Opening Night (1951), published in USA as Night at the Vulcan
• Spinsters in Jeopardy (1954), republished in the USA as The Bride of Death (1955)
• Scales of Justice (1955)
• Off With His Head (1957), published in USA as Death of a Fool
• Singing in the Shrouds (1959)
• False Scent (1960)
• Hand in Glove (1962)
• Dead Water (1964)
• Death at the Dolphin (1967), published in USA as Killer Dolphin
• Clutch of Constables (1968)
• When in Rome (1970)
• Tied Up in Tinsel (1972)
• Black As He's Painted (1974)
• Last Ditch (1977)
• Grave Mistake (1978)
• Photo Finish (1980)
• Light Thickens (1982)

Short Stories

Collected in the book Death on the Air and Other Stories, first published in Great Britain by HarperCollins in 1995:

Roderick Alleyn Stories:

• "Death on the Air"' (1936)
• '"I Can Find My Way Out" (1946 - USA)
• "Chapter and Verse: The Little Copplestone Mystery" (1974 - USA)

Other Stories:

• "The Hand in the Sand" (1953 - USA)
• "The Cupid Mirror" (1972)
• "A Fool about Money" (1973 - USA)
• "Morepork" (1979 - USA)
• "Moonshine" (1936 - NZ)
• "Evil Liver" (script of an episode of the series Crown Court by Granada Television Ltd; recorded in England in 1975)
• "My Poor Boy" (1959)

The book also includes two "biographical" essays written by Ngaio Marsh: "Roderick Alleyn" and "Portrait of Troy".

Non-Fiction

• Black Beech and Honeydew (1965, autobiography)
• New Zealand (1968)
• Singing Land (1974)

Four of Marsh's novels aired on New Zealand television in 1977. Nine were adapted for television as The Inspector Alleyn Mysteries and aired on the BBC between 1990 and 1994.