Margaret Moxon was born on 18 August 1808 in the parish of Sculcoates, Hull, Yorkshire, England, the daughter of Margaret Heaton and her husband, John Moxon, a businessman and banker. She was well educated, and became interested in missionary work while at school. She began her career as a governess in London. On 3 July 1837 at Islington, London, she married George Adam Kissling, a widowed German Lutheran missionary with a young son. They were to have six sons.
After her marriage Margaret Kissling returned with her husband to his CMS station in Sierra Leone, West Africa, to teach at the mission school. In 1840 George Kissling suffered a severe attack of yellow fever, and the Kisslings returned to England with their first son, John. In 1841 George Kissling was ordained an Anglican priest. He was appointed to the New Zealand mission, and the family sailed for New Zealand in the Louisa Campbell, arriving at Auckland on 20 May 1842.
In March 1843 Margaret and George Kissling established a CMS station at Te Kawakawa (Te Araroa), on the East Coast. Like other missionary wives, Margaret Kissling experienced isolation and loneliness. As well as attending to the demands placed on her by her husband's ill health, the care of her children, and two further pregnancies, she started a school for Maori children, and assisted her husband with the daily running of the mission station, taking charge when he was away from home.
Early in 1846 George Kissling became seriously ill and the family returned to Auckland, accompanied by 20 young Maori, 14 female and 6 male, from the East Coast. The Kisslings established a Maori girls' boarding school in buildings which Bishop G. A. Selwyn had purchased from William Spain at Kohimarama (Mission Bay). They hoped to train the girls 'to become Christian Mothers, and probably also help-mates to Christian native teachers.' By December 1846 there were 16 girls attending the school. By 1850 four of the senior pupils had married Maori teachers.
Early in January 1848 the Kohimarama buildings were destroyed by a fire in which Margaret Kissling nearly lost her life while saving some of her husband's papers. The school was continued in a large house in Parnell. To qualify for government grants, Maori boarding schools conducted by church organisations had to provide training in agricultural, domestic and industrial arts, as well as a formal education. To carry out these objects, and to provide financial support for the school, Margaret Kissling organised the New Zealand Female Aborigines Washing Establishment, which took in laundry from Auckland settlers.
In December 1850 a new building for the boarding school was opened by Bishop Selwyn, and named St Stephen's School for Native Girls. Twenty or thirty girls attended. In March 1854 the school received a favourable first report from the government inspectors, William Martin, Andrew Sinclair and Charles Ligar, who wrote: 'No contrast can be more striking and more pleasing than the appearance of these young women as compared with that of the girls in a Native Village.' The girls could 'generally read and pronounce English well.'
Adult male Maori attended St Stephen's as candidates for the ministry, and Margaret Kissling was responsible for the formal and domestic education of their wives and children. She was assisted by Mary Martin and Sarah Selwyn.
Common sense, energy, good health and a forceful personality enabled Margaret Kissling to organise the daily life of the residential school successfully. Her home in Parnell was a haven for visitors, and for the recuperation of the sick. Many missionaries had occasion to be grateful for her hospitality, sympathetic nature, and considerable nursing and sewing skills. Margaret Kissling also taught Sunday school at the Maori church of St Barnabas in Parnell, and assisted her husband with his clerical duties.
When George Kissling suffered a stroke in 1860, he and his wife retired to their own home, not far from St Stephen's, and continued to help with the instruction of the pupils. In December 1856 Margaret Kissling's sister, Mary Jane Moxon, had married the widowed Anglican missionary Thomas Chapman, in Auckland. For some years from 1861 Thomas Chapman, with the assistance of Mary Chapman, took over the management of the school in Parnell. After her husband's death on 9 November 1865, Margaret Kissling continued to live in Parnell with members of her family until her death on 20 September 1891.
The boarding school which the Kisslings established was the forerunner of St Stephen's School, a boarding school for Maori boys at Bombay, south Auckland.