Una Isabel Carter was born on 20 August 1890 at Upper Tutaenui, near Marton, New Zealand, the daughter of Selina Brown and her husband, William Alfred Carter, a farmer. Little is known of Una's early life but it is said she inherited an interest in cooking from her mother, who also taught her a great deal about food.
Despite her lack of formal training Una Carter was holding cookery demonstrations in Wellington by May 1913. At the same time she was employed by the Wellington Gas Company to give cooking classes at its Courtenay Place showroom. There she demonstrated to large audiences the benefits and culinary possibilities of cooking with gas. Later in the year she established a cooking school in Willis Street, advertising for pupils in local newspapers. A course of eight lessons could be had for £1 1s., and classes were held during the day and in the evening to suit both 'young women engaged in business' and women who worked at home. Una became increasingly well known through her work with the gas company, and was called on to judge local cooking competitions. She also undertook demonstration tours of both New Zealand and Australia.
The growing popularity of Una Carter's work and requests from her students for copies of her recipes led to the publication of The national cookery book. Published by 1918, the book contained over 400 recipes and was later reissued, with twice as many recipes, as Una Carter's famous cookbook. This ran to at least 10 editions and included recipes ranging from very basic (how to boil an egg) to more complicated dishes. There were also sections on household hints, such as making soap, and on home remedies for scalds and burns. Carter's recipes emphasised thrift, practicality and the importance of good nutrition. There were 14 recipes for various types of scones, but by far the largest section was devoted to cakes and sweets. Una left the royalties from this book to St Mark's Church School, Wellington.
Una Carter's other book, Home made sweets, was published during the First World War, soon after The national cookery book. Although small (it measured 5.3 by 4 inches), Home made sweets contained over 150 recipes for sweets of all descriptions. In it Carter encouraged her readers to make sweets for New Zealand soldiers stationed overseas, suggesting they send them in small tins so that 'the men can carry them in their pockets and enjoy them when feeling tired and lonely'.
On 31 January 1924 at Wellington, Una Carter married Albert David Stanley, a secretary. After her marriage Una lived in Auckland. She returned to Wellington when Albert Stanley died, and lived in her old home on The Terrace. She demonstrated her cooking at the New Zealand Centennial Exhibition in Wellington and continued doing demonstrations into the 1940s. Although she had no children of her own, she played an important role in her extended family, passing on her knowledge about cooking and distributing her own home-made sweets to visiting nieces and nephews. Most of Una's working life was spent in Wellington and she was best known there, but the considerable sales of her books ensured that her down-to-earth advice came to be relied on in many New Zealand homes.
Una Stanley went to live in England in the early 1950s. She planned to return to New Zealand but died in London on 14 October 1954.