Daisy Elizabeth Platts-Mills was born Elizabeth Platts on 13 July 1868 at Sandridge, Victoria, Australia, the daughter of Emma Walton and her husband, Frederick Charles Platts, an Anglican clergyman. The Platts family was a large one. Emma died when Daisy was young and Frederick remarried. She came to New Zealand in 1880 when her father became vicar of Holy Trinity Church, Port Chalmers. Daisy attended Otago Girls' High School and entered the University of Otago Medical School in her 20s; she gained an MB, ChB in 1900, one of the group of four women who followed the pioneers Emily Siedeberg and Margaret Cruickshank into the medical profession. In 1900 Daisy Platts was one of five women and 706 men on the medical register.
After a brief period as assistant to W. E. Stevens at Kurow in rural Otago, Daisy Platts moved to Wellington in 1901. She returned to Port Chalmers briefly to marry Wellington merchant John Fortescue Wright Mills on 11 February 1902. The couple bought the old Donald Tea Gardens in Karori, and Daisy Platts-Mills, as she now became known, gave birth to three children over the next five years. At the same time she was establishing herself as the first woman doctor in private practice in Wellington.
Tall and striking in appearance, an excellent public speaker and a trenchant writer, Platts-Mills used her talents generously in community affairs, especially those relating to the health and welfare of women and children. For six years from 1912 she was house physician to the children's ward at Wellington Hospital. She also served for two successive terms on the Wellington Hospital and Charitable Aid Board, topping the poll in both elections. She referred to the successful campaign for the reorganisation of the capital's milk supply at this time as 'one of the greatest boons conferred on the children of Wellington'. She was the first president of the Plunket Society in Wellington, and belonged to the Mothers' Union, the League of Mothers, the Women's Christian Temperance Union of New Zealand, the New Zealand Society for the Protection of Women and Children, and the YWCA. She held office to become a past noble grand of the Independent Order of Oddfellows.
Platts-Mills's commitment to community service and interest in public health took her into a local town-planning association and the St John Ambulance Brigade, for which she was a lecturer and examiner, and lady district superintendent. Her work was recognised with a St John war service medal and she was made an officer of the Order of St John. The mix of competence and compassion typical of her was demonstrated during the watersiders' strike of 1913 when she gave her services to alleviate distress among the strikers. More than once she gave evidence before the Court of Arbitration on behalf of girl shop assistants, and she was an office holder in the Women's Borstal Association of New Zealand.
During the First World War Daisy Platts-Mills contributed to patriotic fund-raising as the Tramway Boys' candidate for queen of the Wellington Carnival and was prominent when the prime minister's wife, Christina Massey, held a farewell for nurses leaving for service overseas. She was a founding member of the Women's National Reserve of New Zealand, an organisation that aimed to register the names of all women prepared to give assistance of any kind to their country.
In 1915 Platts-Mills gave up private practice to become the first woman medical officer to the Public Service Commission. She held special responsibility for female staff – a recognition of the influx of women into the public service that began during the war. Her report for 1920 exemplifies both her breadth of view and her brisk attention to detail. Based on evidence gathered on visits to Auckland, Napier, Christchurch and Dunedin, as well as in Wellington, the report argued the need to monitor the health of female public service employees, at the same time warning against too lenient an attitude to sick leave. To foster a congenial work environment, Platts-Mills advocated well-run restaurants, comfortable rest rooms and sick rooms, and outdoor recreation areas. For the many girls of 14 to 16 living and working away from home for the first time, she recommended hostel accommodation, continuing education classes – including practical homemaking – and regular exercise on tennis and fives courts and in the gymnasium. Platts-Mills publicised her general views on health and hygiene in a number of pamphlets and was much in demand as a speaker on these issues.
In 1922 the committee on venereal diseases, appointed by the Board of Health, took evidence on the question of compulsory notification and treatment. Platts-Mills, appearing on behalf of the YWCA, argued in favour of reporting all sufferers by number or symbol and for the naming, compulsory examination and treatment of those 'recalcitrants' who refused to continue with treatment until cured. Despite the opposition of some medical witnesses, these measures were adopted by the committee.
Daisy Platts-Mills was also actively involved in her local community, Karori. The borough council formally thanked her for her dedicated work during the 1918 influenza epidemic. Her sturdy Hupmobile was a familiar sight on the unsealed roads of the area, and the headmaster of the local school called on her whenever accidents occurred. Gifted musically, she was for many years organist at St Mary's Anglican Church.
In 1934 Daisy Platts-Mills and her husband retired to Whakatane and later to Auckland. Two of their children had already embarked on notable careers. Their daughter Adah became a doctor in New Zealand, and their son John, a member of the House of Commons. John senior died in 1944. Daisy survived him for 12 years, dying at Auckland on 1 August 1956.