Agnes Elizabeth Lloyd Bennett was born on 24 June 1872 at Neutral Bay, Sydney, Australia, the sixth of seven children of William Christopher Bennett, an exceptionally able engineer and commissioner of roads and bridges for New South Wales, and his wife, Agnes Amelia Hays, an intelligent woman of strong character. The young Agnes enjoyed a happy childhood in the garden, bush and beach beside her home until her parents, believing that schools in Sydney were inadequate, decided that her mother should sail with the children for England in February 1878. They settled first in Cheltenham, where Agnes attended Cheltenham Ladies' College; she was proud of her connection with this school and its headmistress, Dorothea Beale, a pioneer in girls' education. In late 1879 they moved to Dulwich, North London, where the girls attended the high school run by the Girls' Public Day School Company.
Their mother's death from smallpox in June 1881 led to the children's immediate return to Sydney. Agnes became a pupil of Abbotsleigh girls' school from 1885 to 1887 and of Sydney Girls' High School from 1888 to 1890. After winning a state scholarship she matriculated at the University of Sydney, where in 1894 she graduated with the degree of BSc with honours in geology and biology. Reputed to be the first woman to gain a science degree with honours at the university, she found that the positions for which she applied went to men with inferior qualifications. After a year as a governess in the backblocks of northern New South Wales, she left to study medicine at the Medical College for Women in the University of Edinburgh, Scotland, arriving early in 1896.
Agnes Bennett graduated MB, ChM in 1899. Afterwards she worked as resident medical assistant at Stirling District Asylum, Larbert, near Edinburgh for a year before returning to Sydney in 1901. Prejudice against women doctors hampered her attempt to establish herself in a practice there and she soon accepted a position as resident medical officer at Callan Park Asylum.
When given the opportunity to buy the practice of Dr Isabella Watson in 1905, Bennett moved to Wellington, New Zealand, and spent the next few years building up the upper Willis Street practice. In 1908 she was appointed medical officer to St Helens Hospital, Wellington, and in 1910 honorary physician to the children's ward in Wellington Hospital. Her work at St Helens allowed her to develop her interest in obstetrics and provided her with data on breastfeeding which was the basis of her thesis for the degree of doctor of medicine, obtained from the University of Edinburgh in 1911.
Always quick to champion educational opportunities for women, she became involved in two controversies with medical authorities who opposed women's higher education on the grounds that the health of the nation's future mothers would be impaired by the stress of advanced education. She and Dr Emily Siedeberg challenged the views of Dr Ferdinand Batchelor and Dr Truby King in 1909 and she undermined King's position at the Australasian Medical Congress in Auckland in 1914.
In 1915, after the outbreak of the First World War, Bennett offered her services to the New Zealand government, but they had no interest in employing a woman doctor. Instead, she sailed for Europe to serve with the French Red Cross. However, while travelling through Cairo she was offered employment in the New Zealand Medical Corps, with the status and pay of captain but without a formal commission.
After working in military hospitals in Cairo for almost a year, Bennett resigned and left for England in April 1916. She was appointed commanding officer of the 7th Medical Unit, Scottish Women's Hospitals for Foreign Service, staffed by women and financed by the National Union of Women's Suffrage Societies. From August her field hospital was attached to the Serbian army. The work was strenuous and conditions were often harsh and dangerous but Agnes Bennett, tall, strong and active, enjoyed using to the full her skills of organisation, leadership and tact. After an attack of malaria led to her resignation in October 1917, Bennett received the Order of St Sava, third class, of Serbia and the Cross of Honour of the Serbian Red Cross. In 1917 and 1918 she was medical officer on the troop-ships Wiltshire and Paparoa and in 1918 on the cargo ship Essex. She worked in the Royal Infirmary, Glasgow, during the influenza epidemic of 1918, and then at a military hospital near Southampton.
By 1920 Bennett was back in Wellington, where she resumed her medical practice and her work at St Helens Hospital. The instruction of midwives was an important part of her duties, her main concern being the reduction of maternal mortality in childbirth and the stillbirth and neonatal death rates. Through the enforcement of good antenatal care, strict asepsis in deliveries and new methods in the tending of newborn babies, she achieved her aims and by her results provided a model which was influential throughout the country. She retired in 1936.
Bennett had given up her medical practice in the city in 1930, but her retirement provided her with fresh opportunities for service. During the early stages of the Second World War she was active in organising the Women's War Service Auxiliary. In September 1940 she sailed as medical officer on the Port Alma for England where she worked first with the Women's Voluntary Services for Civil Defence and later as a medical officer in hospitals. After returning to New Zealand in 1942, she travelled around the country giving lectures to servicewomen, mainly on sex education.
In 1947 Bennett answered a call for a doctor to work in the Chatham Islands during the illness of the resident medical practitioner. Her five weeks there under unpleasant winter conditions, travelling usually on horseback, won her national fame. It seems likely that the appointment of OBE the following year was partly prompted by this work, remarkable for a woman of 75.
Throughout her busy life Bennett found time to travel overseas to extend her knowledge, work, make new contacts and present papers at medical conferences. The first president in 1922 of the Wellington branch of the New Zealand Federation of University Women, she attended a conference in Poland in 1936 as a federation delegate and for many years was active in the Wellington branch. Her retirement included a period of work in the flying doctor service in Queensland in 1939.
Agnes Bennett died in Wellington on 27 November 1960; she had never married. An energetic and highly capable woman whose work in maternal and infant health was of national significance, she believed in serving others. In 1955 she gave money to the University of Sydney to found an aeronautical laboratory in memory of her parents, and left a further sum to the university in her will. She also donated the larger of her two houses in Lowry Bay to the Women's Division of Federated Farmers of New Zealand for use as a holiday home and bequeathed her second house to the same organisation.