Mary Edith Clarke was born in Waimate North in the Bay of Islands on 23 September 1888, the daughter of Marsden Clarke, a grazier, and his wife, Frances Emily Stuart. Mary's great-grandfather, George Clarke, had arrived in the Bay of Islands as one of Samuel Marsden's lay missionaries in 1824. After the death of Marsden Clarke in 1889, the family went to live in Napier with their maternal grandfather, Edward Stuart, the bishop of Waiapu.
Mary Clarke had an 'ideal childhood', she and her sister sketchily supervised by an elderly nurse while their mother earned an income teaching music. Both girls became very good horsewomen. In 1900 Mary was sent as a boarder to Napier Girls' High School. After two years the Clarke fortunes improved, Frances Clarke gave up music teaching and the family moved to Auckland. Mary attended Auckland Grammar School, where her brother Edward had taken a job as junior master, then went to Auckland University College in 1905 to study English, French and History.
On graduation Mary Clarke took a job teaching at Gisborne High School, but after hearing she had won the John Tinline Scholarship in English she returned to Auckland in 1910 to study for an MA in English and French, eventually graduating with first-class honours. In 1911 she went teaching at Christchurch Technical College and began a lifelong association with her second cousin Marguerita Mulgan and her husband, Alan. After little more than a year in Christchurch she returned to Auckland to look after her brother, whose wife had just died, and began to study sciences, but soon accepted a position teaching English at Thames High School. At the end of the year she went on holiday with her brother to the South Island where she became possibly the first woman to climb the Remarkables.
In 1913 Frances Clarke, Mary's elder sister, married David Scott, a farmer; Mary and her mother went to Gisborne to stay with her. Mary met David's brother Walter, whom she married at Te Karaka on 12 October 1914. Immediately after their marriage the Scotts moved to a backblocks sheep farm, Strathallan, on the slopes of Pirongia Mountain in the King Country. They were joined shortly afterwards on the next-door farm by Frances and David Scott.
The Scotts farmed at Strathallan for 13 years in very primitive and isolated conditions, struggling with bush sickness (caused in livestock by a mineral deficiency of the soil) and natural disasters. In 1917 and 1918 there were two fires: the first destroyed their house and all their possessions, the second swept through the bush, burnt all the fences and new pastures and killed most of the stock. The Scotts reluctantly diversified into a small dairy herd, but this was not the answer to farming at Strathallan, and in 1927 they moved with their four children to a new farm at Ngutunui, nearer Te Awamutu.
Education was a considerable problem in such an isolated area. The two older children were sent to boarding school, but the legacy from a relative that allowed this ran out by the early 1930s. Mary took a job as a librarian in Te Awamutu; this provided a house to live in and she could send the two younger children to school in town. They returned to the farm on weekends.
In the late 1920s Mary Scott decided to start writing, sending articles and stories to magazines and newspapers. In 1930 she was the 'Annual Discovery' of the New Zealand Artists' Annual and about this time she began to contribute a weekly item to the Dunedin Evening Star, for which she was to write for almost 50 years. A series of amusing stories based on her life in the bush, beginning with 'Barbara bakes', became Scott's popular Barbara books. During her period at the Te Awamutu library she contributed 14 articles a month to various papers as well as writing her first two novels, published under the pseudonym Marten Stuart: Where the apple reddens in 1934 and the following year And shadows flee. These were historical romances set in the far north of early nineteenth century New Zealand. Her later novels, published under her own name and set in the contemporary King Country, were realistic and humorous. Scott said that she was the first woman to write about backblocks farming and she was probably also the first woman to write romantic comedies firmly grounded in New Zealand rural life. This lifted her novels from the category of mere romance, and she became widely read both in New Zealand and overseas.
Scott's first bestseller was Breakfast at six (1953), which was reprinted six times in the three years after its publication. Until 1956 her novels were published in London, but from Families are fun by Paul's Book Arcade, Hamilton. Many of her books were translated and several were bestsellers in Germany. As well as five collections of Barbara stories, Scott wrote three collections of plays for country women's institutes; 33 novels, including five thrillers written with Joyce West; two novels as Marten Stuart; and a monograph under the pen-name J. Fiat. This prodigious output continued under the relentless labour of contributing regular articles to newspapers and journals such as the Manchester Guardian and the Evening Star. From 1953 she produced almost one novel a year until 1978.
In August 1958 the Scotts moved off their farm at Ngutunui and it was taken over by their son Stuart; they settled on a sheep farm at Arapuni. After Walter's death in March 1960, Mary Scott moved to Howick, and then lived with one of her daughters at Tīrau. She died at Tokoroa on 16 July 1979.
Scott's autobiography, Days that have been (1966), and her serious novel, The unwritten book (1957), tell a grimmer story of life in the bush than her popular novels, but all her work stresses the value of bush community and explores the tensions between town and country. Scott often referred to her 'fatal facility', a term used of her writing by one of her university teachers, and her work was typecast as 'light'. But she represents something rare in New Zealand literature: a highly successful, prolific, comic and realistic woman writer.