Frances Ann Carkeek was born on 18 June 1840 at Sydney, Australia. She was the daughter of Martha Piotti and her husband, Stephen Carkeek, commander of a revenue cutter. The family moved to Nelson, New Zealand, after Stephen Carkeek was appointed sub-collector of customs there in 1842.
Little is known about Frances's formative years, but she evidently enjoyed a good education. She may have attended dame schools in Nelson and Wellington, for she referred to them later in life when discussing the role of women in early colonial education. As an adult she was a prodigious reader and classical scholar, and had an abiding interest in educational matters.
The Carkeek family moved to Wellington in 1849 when Frances's father was appointed collector of customs. In 1851 he became a member of the Legislative Council of New Zealand. It was in Wellington that Frances met her future husband, John Tiffin Stewart, who was appointed provincial engineer in 1861. They were married at St Peter's Church, Wellington, on 22 November 1865. Five years later they moved to Foxton, at first living in a surveyor's tent while a large house was built. Five daughters and five sons were born there.
When John Stewart retired as district surveyor in 1889 the family shifted to Wanganui. They built a house on a 17-acre property at Aramoho, and named it Haumoana. The Stewarts became an important family in the area. They hosted garden parties and balls for the town's social élite, their sons attended Wanganui Collegiate School, and their daughters were taken on world trips. Frances was also active in the community. She was president of the local division of the St John Ambulance Association, and was a member of the management committee for the Wanganui exhibition held in 1894, which raised money for the town museum; her husband was vice president and then president of the museum's board of trustees.
In her many letters to newspapers, Frances Stewart is revealed as a prominent social activist. She saw herself first and foremost as a mother, often signing her letters 'A Mother' or 'Indignant Mother', and had a keen interest in anything concerning children. She was perhaps best known for her association with the Wanganui Orphanage, which was opened in August 1889 as a non-denominational Protestant home. She was also the first superintendent of the new Anglican Sunday schools at Christ Church and Aramoho, and donated land for the establishment of Wanganui Girls' College. In 1908 the Stewarts shifted into town. When their baby grandson became dangerously ill and was treated successfully by Frederic Truby King, their gratitude led them to bequeath their house in Plymouth Street for the care of children. It became the Stewart Karitane Home.
Frances Stewart championed the right of women to participate in public life, and became the first woman member of a hospital board. In 1896 she stood for election to the Wanganui Borough Council, hoping that once elected she would then be nominated to the Wanganui Hospital Board. She based her platform on women's experience and knowledge. This reflected the increasingly widespread view that women would bring superior qualities to bear on public activities, both through their social sympathies and as an extension of their nurturing role in the family and home. She failed to get elected, but was nevertheless appointed a representative on the hospital board for the Wanganui and Marton boroughs for 1897 and 1898, despite the objections of some councillors. In 1899 she retired because she found it difficult to achieve anything as a lone female voice, but in 1903 was reappointed for a year to represent Wanganui. On the board she campaigned for better training for nurses and improved conditions at the old people's Jubilee Home, where she had been appointed an official visitor in the 1890s. In 1910, when board members were for the first time elected rather than nominated, she tried, unsuccessfully, to regain a seat, stating, 'I consider myself a pioneer for my own sex, hoping that other women will have the courage to come forward the next time there is an election.'
Frances Stewart also advocated women's participation in church and school affairs, and supported prohibition and women's suffrage. Nevertheless, she felt that there should be limits to women's public activities. She endorsed mild and private action, and as a woman of social standing claimed a freedom for her peers that she was less happy to see extended universally. She felt it would be a mistake to grant the vote indiscriminately to all women as to all men, and believed that the franchise leagues formed in the 1890s did not represent the more sober-minded women of New Zealand. She predicted 'plenty of domestic unhappiness' if women were granted economic independence. Women should be educated, but to better fulfil their roles as wives and mothers.
Frances Stewart died at her home on 12 November 1916, three years after the death of her husband.