Janet Speed was born on 31 January 1864 in Whanganui, New Zealand, the fifth of eight children of James Speed and his wife, Janet Montgomery. James had business interests and land at Whanganui, but soon after Janet's birth the family moved to Picton. Her father died when she was 10; otherwise, little is known of her early life and education. In 1887 she began nursing training at Wellington District Hospital, and worked there until 1894. Soon after, she returned to Picton.
Janet Speed was one of at least 31 New Zealand nurses who served in the South African War between 1899 and 1902. Some went with official approval but none were paid by the New Zealand government. Local patriotic committees raised funds to send small groups of nurses; others joined the Army Nursing Service Reserve in England or travelled to South Africa at their own expense. Janet Speed was among those who paid their own fare; once in South Africa in late 1900 she joined the nursing reserve and her salary was paid by the British government. When the war ended in 1902 she received the King's South Africa Medal.
Shocked at the inefficiency of the hospitals she had served in during the conflict, Speed resolved to further her knowledge of military nursing. She travelled from South Africa to England in 1902 and, at her own expense, undertook a course on the subject at the Royal Victoria Hospital, Netley. Returning to Wellington in 1903 she became associated with the newly formed St John Ambulance District Nursing Guild, a home-nursing service for the poor, and in July 1903 was elected an honorary nursing sister. At the Holy Trinity Church, Picton, on 6 April 1904, Janet Speed married David Welsh Gillies, a surveyor with the Lands and Survey Department. The couple lived first at Blenheim, then at Nelson. Although she had no children, it seems that Janet Gillies no longer practised as a nurse after her marriage.
Nevertheless, she remained interested in nursing issues. In 1907 Princess Christian, president of the Army Nursing Service Reserve, wrote to the governor, Lord Plunket, suggesting the formation of a New Zealand branch. Janet Gillies gave her enthusiastic support to the idea and offered her services as matron in chief to the minister of defence, Joseph Ward. On 14 May 1908 the New Zealand Medical Corps Nursing Reserve was gazetted, and on 30 August 1908 Janet Gillies was appointed matron in chief. The position brought official status but no salary, and was essentially administrative. However, Janet Gillies found herself in the anomalous situation of being head of a nursing reserve with no nurses. Despite engaging in a vigorous correspondence with the minister of defence, she was blocked in her attempts at recruitment. It was necessary for her to travel in order to organise the reserve, but she was unable to do so because she was not paid expenses. Her suggestion that a subcommittee be set up to oversee the appointment of nurses was ignored and her request for a meeting with the minister was denied. In vain she protested that 'the affairs in connection with the Nursing Reserve are very unsatisfactory'.
Janet Gillies seems to have met resistance because she was married, not actively nursing, and living outside Wellington. It was felt that she was out of touch with 'the nurses best fitted to take responsible charge', and that the reserve, like other nursing services, should be administered by the Department of Hospitals and Charitable Aid. In 1909 the acting director general of medical services, James Purdy, recommended to the Defence Department that the inspector general of hospitals and charitable institutions, Thomas Valintine, would be the best person to administer the nursing reserve. Then, in the event of war, the nurses already in the public hospital system could easily be transferred to a military medical force. He also recommended that Janet Gillies be asked to resign as matron in chief. In the face of such opposition she had no option but to step down, which she did on 29 June 1910. The experience left her deeply disappointed, but she did not give up her vision.
She and her husband left Nelson within a few years, moving north and eventually settling in Auckland. In June 1913 Janet Gillies wrote to the new minister of defence, James Allen, again offering to set up a nursing reserve. It was suggested that she contact Valintine, but she insisted that the reserve was a military organisation and should be formed at the initiative of the defence authorities. In early 1914, shortly before departing on a trip to England, she again wrote to Allen asking him for a formal response to her offer, as she wished to inform the British nursing reserve of the situation when she arrived in England. She was told that her offer had been declined, and that she had no authority to contact the British reserve on behalf of the New Zealand government.
On returning to New Zealand, Janet and David Gillies again lived in Auckland, where David died in 1930. Janet Gillies died there on 24 July 1947. Her efforts to set up an army nursing service in New Zealand went largely unrecognised during her lifetime. However, her plans were put into practice during the First World War, when under the direction of her successor as matron in chief, Hester Maclean, nurses were recruited for the New Zealand Army Nursing Service. These nurses, who served with distinction during the war, proved the worth of an organised military nursing system for New Zealand's defence forces.