She is known primarily for her character Inspector Roderick Alleyn, a gentleman detective who works for the Metropolitan Police (London).

She studied painting at the Canterbury College (NZ) School of Art before joining the Allan Wilkie company as an actress in 1916 and touring New Zealand.

[3] In addition she and one of the friends with whom she had come to London opened Touch and Go, a handicraft shop that sold items such as decorated trays, bowls and lampshades.

[2] Agatha Chistie held that both Muriel Spark and Ngaio Marsh wrote a very good detective story.

Notably, Colour Scheme includes Māori people among its cast of characters, unusual for novels of the British mystery genre.

[16] This novel is said to further subvert the genre by incorporating elements of spy fiction and providing a veiled critique of the British Empire.

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.

She lived to see New Zealand develop a viable professional theatre industry having realistic Arts Council support, with many of her protégés to the forefront.

[20] Her home, now known as Ngaio Marsh House, in Cashmere, a suburb of Christchurch on the northern slopes of the Port Hills, is preserved as a museum.

[2] She enjoyed close companionships with women, including her lifelong friend Sylvia Fox, but denied being lesbian, according to biographer Joanne Drayton.

[5] "I think Ngaio Marsh wanted the freedom of being who she was in a world, especially in a New Zealand that was still very conformist in its judgments of what constituted 'decent jokers, good Sheilas, and 'weirdos'", Roy Vaughan wrote after meeting her on a P&O Liner.

New Zealand art historian Joanne Drayton's biography, Ngaio Marsh: Her Life in Crime was published in 2008.

[42] In the 1990s the BBC made radio adaptations of Surfeit of Lampreys, A Man Lay Dead, Opening Night, and When in Rome starring Jeremy Clyde as Inspector Alleyn, and in 2010 Death and the Dancing Footman featuring Nigel Graham.