Ada Gertrude Paterson was born at Caversham, Dunedin, New Zealand, on 6 June 1880. She was the daughter of Margaret Smith Ayton and her husband, James Paterson, for many years librarian at the Dunedin Athenaeum and Mechanics' Institute. Ada completed her secondary education as dux in 1898 of Otago Girls' High School, then went on to study medicine at the University of Otago, graduating in 1906. After postgraduate study at Dublin University, around 1908 she commenced general practice in Picton.
There Paterson demonstrated her ability to command affection as well as respect from a wide range of individuals. A farewell social held for her in 1912 was 'one of the most largely-attended and enthusiastic gatherings ever held in Picton'. Representatives of Catholic and Protestant church groups, the Girls' Friendly Society (of which she was a member), the hospital board and local bodies eulogised her as a 'people's doctor', kindly, supportive and ever available to help. The local Maori community presented her with valued gifts, including mats, a greenstone pendant and an amokura feather. Nurses at the local hospital and members of the New Zealand Women's Christian Temperance Union made their own presentations.
Paterson left to join the school medical service under the Education Department in August. Initially, she was sent to Dunedin as one of New Zealand's first four school doctors. This involved her in the physical examination of thousands of schoolchildren annually. Transferred to Wellington in 1916, she continued to show in her annual reports a special concern for the health of girls who, she believed, were reared under considerably less advantageous circumstances than boys. She was a firm advocate of preventive health-care, noting that with children 'to-morrow is never as good as to-day. The body in childhood is plastic and the mind impressionable, and the records that are printed upon them last throughout life.'
In late 1921, shortly after the transfer of the school medical service from Education to the Department of Health, Paterson took a year's leave of absence to investigate child health and welfare work in Australia, Britain and North America. She was impressed by health education programmes overseas, and her visit intensified her existing interest in 'mentally backward' children. On her return to New Zealand she promoted special classes and schools for such children, and also ran informal psychological clinics for children exhibiting behavioural problems; Paterson was a pioneer in her concern for children's minds, as well as their bodies. In 1924 she served on the Committee of Inquiry into Mental Defectives and Sexual Offenders in New Zealand. The questions she put to professionals making submissions show her as a woman of her time, sharing in contemporary concerns about the threat to society posed by the 'feeble-minded'.
From 1923 Paterson was director of the Health Department's Division of School Hygiene, one of two women among seven (later six) divisional directors. School medicine was then regarded as the Cinderella of the health services. Paterson did her best to raise its public profile, ceaselessly addressing school boards, service clubs and women's organisations, writing articles and promoting child health among her extensive circle of acquaintances. She was widely recognised as an effective mediator, able to win parents over when a tactless school doctor or nurse had upset them, and teachers when they resented the intrusion and disruption of school medical inspections. Paterson saw her own role as that of a 'fire extinguisher', and her talent for arbitration was used to solve at least one industrial conflict involving women – at the Westfield Freezing Works in 1934. The senior woman public servant of her day, she was often consulted about potential women appointees to government positions.
Ada Paterson was keen to see school medical inspection extended beyond the primary schools, but the financial and staffing cuts of the depression limited new undertakings. One venture she did feel able to promote during the 1930s was the children's health camps movement. Initiated by Elizabeth Gunn in 1919, health camps were taken up by voluntary associations all over the country during the depression years. Unlike Gunn, Paterson had the personal qualities to direct, with tact and sensitivity, the strong-minded and often idiosyncratic personalities who were attracted to health committees. She personally founded the Wellington Children's Health Camp Association, and was the driving force behind the establishment of Raukawa Children's Health Camp at Otaki in 1932. Paterson badgered other departments for assistance, arranged overdrafts with banks, saw the police when health camp donation tins were rifled, recruited local worthies onto the health camp committee, and promoted harmony among staff. As the first permanent, year-round children's health camp, Raukawa (later known as the Otaki Children's Health Camp) provided a model for subsequent developments. In 1936 Paterson's diplomacy helped achieve a national federation of children's health camps closely aligned with the Health Department.
Paterson's influence extended beyond the Health Department. She was an official visitor to the women's borstal and frequently attended the juvenile courts. Through her membership of numerous women's organisations she built up a network of friends and supporters and was an early committee member of the New Zealand Federation of University Women. She represented New Zealand at the 1935 conference of the International Labour Organisation in Geneva, where she spoke on the scientific value of agricultural foodstuffs in diets. This trip enabled her to visit further child health and welfare institutions in Britain and Europe, including the famous open-air school run by Auguste Rollier at Leysin, Switzerland.
The following year Ada Paterson was diagnosed as having cancer and underwent a mastectomy. She died in Wellington on 26 August 1937. Tributes to 'Dr Pat' were heartfelt, especially those from nurses and other women professionals. They extolled her dry wit, broad-minded tolerance, wise counsel, and ability to listen to others while at the same time convincing them that her summing up of a situation was right. She is commemorated by Ada Paterson memorial bells at four of New Zealand's health camps.