Born Esther Loreena Gordon, Mary King was adopted at the age of 13 months by Sir Frederic Truby King of New Zealand, the Superintendent of a mental hospital who established scientifically formulated doctrines on nutrition and infant care to reduce the death rate among infants. He founded the Karitane Home for Babies in Dunedin in 1907 and established the Plunket Society (originally called the Society for the Health of Women and Children) as a way of ensuring home visits by nurses for newborn babies.
King was educated at Nelson Girls' College, and at the age of 16 she was baptised in the Presbyterian Church. She trained as a kindergarten teacher and as a nurse, but spent much of her early life as an assistant to her father. A journey to France with him when she was about 26 led to her conversion to Catholicism.
She came to Australia in about 1930 on Plunket Society business and stayed. She lived in Sydney and South Australia. She married RAAF Flight Lieutenant Anthony (Tony) H. White in 1945, and they had two sons, Michael and Stephen. When they first married she lived with her husband's family in Hawthorn, but when her husband retired from the Air Force he took up forestry, and they lived in 'forestry areas' in the South East of South Australia, and in Aldgate. She was a friend of the artist Gwen Barringer.
King began writing at school, and was still writing until the age of about 90, when her increasing blindness made this very difficult. She had a short story published, but poems were the form she considered she 'was here to do'. She wrote a great deal about her faith and the church, and published in the Melbourne Advocate and Catholic periodicals including the Monstrance and the Southern Cross.
As well as her poetry, King wrote a book on health care of infants, Mothercraft, that ran to at least 17 printings with an international publisher, a weekly column on childhood and hints for mothers in the Australian Woman's Weekly, and a biography of her adoptive father, Truby King, the Man.
In later years she and her husband lived in Tusmore. In 1997 Tony King died of cancer, and in early 1998 King moved into the Tappeiner Court Nursing Home in Norwood where she died in 2002.