Janet Munro was born on 31 January 1883 in Glasgow, Scotland, to Mary McLean, a housekeeper, and William Munro, an iron foundry warehouseman. Her parents married four years later. Janet sometimes used her maternal grandmother's surname, Henderson, as a middle name. She was educated in Glasgow and became a teacher of orphaned or abandoned children. She was also influenced by the writings of the popular socialist Robert Blatchford.
On 25 November 1903, in Glasgow, Janet Munro married widower Frederick George Kemp, a merchant's cashier; they had one son, Harold. In 1909 the family emigrated to New Zealand, arriving in Auckland in August. Frederick found work as a clerk.
The Kemps mixed with other socialists and in 1911 met a recently arrived Scot, Peter Fraser. Janet was 18 months older than Peter and he was attracted by her intelligence, her gentle voice and interest in socialist literature. The Kemps' marriage eventually failed – Frederick's drinking was possibly a factor – and by 1918 Janet and the teetotal Fraser were living in Wellington. Fraser was elected the member of Parliament for Wellington Central in a by-election in October 1918. The pair worked together as volunteers in the flu epidemic in November. On 4 October 1919 the Kemps were divorced, and on 1 November Janet and Peter were married in the Wellington Registrar's Office.
Janet Fraser became active in politics as the first secretary of the Wellington women's branch of the New Zealand Labour Party, formed in 1920. A voluntary health worker, she was appointed to fill a vacancy on the Wellington Hospital Board in January 1925. She spent 10 years on the board, topping the poll in 1933. Although known for her kindnesses to those in need, she could also fight for her beliefs. Her friend Margaret Thorn said of her, 'Janet Fraser was pure intellect…She stood up to the conservative members of the Hospital Board; the conservative mind in power is a tough commodity’.
Health, education and welfare issues were to concern her throughout her life and led to a series of official appointments: in December 1926 she was appointed one of the first women justices of the peace, in 1927 an associate of the Children's Court, and in 1929 to the newly formed Eugenics Board, whose duties included keeping a register of 'mentally defective persons'. She was also an official visitor to the Porirua Mental Hospital. Fraser was involved in many women's organisations, in particular the League of Mothers, the New Zealand Society for the Protection of Women and Children, the Plunket Society, the Women's Borstal Association of New Zealand, and the New Zealand Federation of University Women. She was also interested in the welfare of Polish and Chinese refugee children.
In 1935 Peter Fraser became minister of health in the first Labour government, but it was Janet who had much of the expertise. She was appointed to a committee of inquiry into abortion, followed by one into maternity services which spent many months conducting hearings throughout New Zealand. Both committees investigated a wide range of social, economic and health issues. As a result the government brought in measures to provide financial support for maternity services and child-rearing.
Janet Fraser had a room next to Peter's in Parliament – ostensibly to look after her husband, who was known to work long hours – but she also undertook research for him and vetted visitors. Dr Doris Gordon was one who realised the value of lobbying Janet to promote her views on maternal health. The Wellington Children's Health Camp Association made her one of their vice presidents.
Janet Fraser frequently travelled with her husband, both before and after he became prime minister in 1940. In 1935 they attended the conference of the Empire Parliamentary Association in London and visited several other countries. Once they travelled to a conference in Australia on a flying boat – a novelty at the time. In 1944 they were in London for the Empire Conference of Prime Ministers. On her return from these trips Janet was in demand to speak about her experiences. She commented on employment and welfare policies, housing developments, child health, justice systems and the position of women in the countries she visited; she showed a particular interest in women's work in non-traditional areas and (during the war) their war work. In 1936, she spoke of women in England working in areas such as property management, engineering and architecture. Her talks and interviews had a large audience. The Frasers also enjoyed the theatre and orchestras, and Janet was extremely well read. Her influence may have contributed to the Labour government’s many initiatives in arts funding.
During the Second World War a co-ordinated approach to the women's war effort became necessary and Janet Fraser was appointed head of the Dominion Central Executive of the Women's War Service Auxiliary. In this capacity she made many speeches and broadcasts. When Eleanor Roosevelt, wife of the United States president, visited New Zealand in August–September 1943 on a goodwill tour, Janet escorted her.
By this time her health was failing, and on 7 March 1945 she died in Lewisham Hospital, Wellington, of the tuberculosis from which she had suffered for 12 years. She was survived by her husband and son and was accorded a large state funeral before her burial in Karori cemetery. As patron of the Te Ropu o te Ora Women's Health League she had been connected with the effort to build a hostel to accommodate Maori visitors to Rotorua; the Janet Fraser Memorial Guest House was opened by Peter Fraser on 30 August 1948. Because of her work for Maori, she was known as 'Te Whaea o te Katoa' (the mother of us all).
Janet Fraser was tall, thin, dark-eyed, dignified and gracious. To her granddaughter, Alice, she was loving but proper – not the sort of grandmother you could hug with floury hands. Her lifelong concern for the poor and disadvantaged and her lively interest in health matters and women's concerns made her an important adviser to her politician husband.