Jane Neill Erwin was born in Fendalton, Christchurch, New Zealand, on 25 January 1890, the daughter of Robert Erwin, a Presbyterian clergyman, and his wife, Esther Neill. Always called Jean, she had three brothers and two sisters. They were all indoctrinated with the concepts of duty and service to others. Her niece recalled that Jean 'was a true daughter of the Manse. She worked quietly for good causes.' In 1909 she joined the St John Ambulance Brigade and in 1914 passed the state examination and became a registered nurse at Christchurch Hospital.
On 6 July 1915 Erwin enlisted in the New Zealand Army Nursing Service and immediately afterwards went overseas. On 23 October that year, while sailing on the troopship Marquette as a staff nurse with other personnel of No 1 New Zealand Stationary Hospital destined for Salonika, Greece, a torpedo struck. About 15 minutes later the vessel sank in the Aegean Sea with the loss of 167 lives, including 10 New Zealand nurses. Along with other surviving New Zealand nurses, on 29 October Erwin left Salonika for Alexandria, where she was attached to various imperial general hospitals, including the hospital ship Goorkha. In October 1916 she went to Brockenhurst, England, where her brother Jack, who had lost an arm, was a patient. In 1917 she was promoted to sister and she was there during the influenza epidemic of 1918–19. She returned to New Zealand and was demobilised on 1 February 1920.
In 1922 Jean Erwin trained as a masseuse at Dunedin Hospital and chose this as her field of specialisation. Between the wars she kept up her military nursing in the Territorial Force and was involved in administrative work, tours of duty, and special parades in Christchurch and Government House, Wellington, always showing her pride and interest in the young women under her care. Her inspections put an emphasis on health and hygiene as well as the comfort of girls who were away from home.
At the beginning of the Second World War she applied for a nursing position abroad and was bitterly disappointed to be informed that she was well over the age limit for overseas service, besides having done no general nursing for some years. However, when the New Zealand Women's Army Auxiliary Corps was formed in 1942, Jean Erwin was appointed to the position of commandant, Southern Military District, with the rank of senior commander (equivalent to major). A prolific letter writer, she expected prompt replies and kept in touch with those of her command who went overseas.
Jean Erwin relinquished her appointment in March 1945 and retired in April after almost 7½ years of army service. In June she was appointed an MBE (military division). By 1962 she was an elder of Knox Presbyterian Church, Christchurch, and she took a deep interest in church affairs and causes such as the New Zealand Crippled Children Society. She never married, although the family was intrigued by the little diamond ring she always wore.
A tall, slim woman with a fair complexion, hazel eyes and light brown hair parted in the middle, Erwin had a stern though kind manner. She was quiet and unassuming, firm in her decisions, and had many elderly friends whom she visited regularly on her old bicycle, which often needed repairs. In 1968 she and one other Marquette survivor unveiled a window in the Nurses' Memorial Chapel at Christchurch Hospital. Jean Erwin died at the hospital on 24 July 1969.