Constance Alice Barnicoat was born on 27 November 1872 in Richmond, Nelson, New Zealand. She was the last of seven children of Rebecca Lee Hodgson and her husband, early farming settler John Wallis Barnicoat, a member of the Nelson Provincial Council and of the Legislative Council. As the youngest by eight years, Constance was brought up virtually as an only child, especially after the early deaths of her nearest sister and a brother. She became an excellent horse rider, and received a classical education at home. Her parents kept in touch with the outside world through English periodicals.
Constance Barnicoat spent 1888 and 1889 at the Nelson College for Girls before enrolling for a BA at Canterbury College. Academically she excelled, particularly in English, taught by Professor John Macmillan Brown, who became a lifelong friend. Graduating in 1895 she worked in Wellington as secretary for nearly three years to F. H. D. Bell, member of the House of Representatives. In 1896 she was reputedly the country's first official female shorthand reporter, for a Legislative Council committee investigating the affairs of the Bank of New Zealand.
Barnicoat had obtained Pitman's first-class certificate in shorthand in 1895, and in May 1897 sailed for England for further training at the Metropolitan School for Shorthand and Languages, London, where she won a prize for first place in French and German. She could read Italian and Spanish, later becoming a fluent Spanish speaker through her travels. Her linguistic ability was an invaluable asset to her employer from 1898, W. T. Stead, founder–editor of the Review of Reviews. She accompanied him as secretary and interpreter to the 1899 Hague Peace Conference, and began reviewing foreign-language books for the Review, as well as free-lancing for the Christchurch Weekly Press and English journals.
In 1902 and 1903 Constance Barnicoat visited New Zealand. During her nine-month stay she was one of three women in a party making a crossing of the Copland Pass near Mt Cook. This formed the subject of the first of her articles about her mountaineering achievements. From the start she wore trousers in the mountains, which was uncommon at the time, and in Europe she made trips alone with male guides.
Returning to London, she joined the reviewing staff of the Review of Reviews. Her criticism of the parochialism, political affairs and lack of hard work of New Zealanders riled local commentators, who referred to this outspoken young woman as 'a first class scold'. She also instituted the Barnicoat Essay Prize for the boys' and girls' colleges in Nelson, to encourage the study of contemporary world history, an area in which she considered colonial education to be lacking.
Her mountaineering feats, however, earned the comment that 'The modern learned young woman…is much more likely to achieve things by training her muscles as well as her mind'. These expeditions included a 1905 ascent of the Ailefroide in the Dauphiné Alps, France, a 1907 trip to the Caucasus, and a 1911 winter ascent of Switzerland's Grosser Schreckhorn – her greatest achievement. Barnicoat was also an intrepid traveller to isolated locations in South America, and later visited North America, Scandinavia and the Middle East.
Through a mutual love of mountaineering and journalism she met journalist and lecturer Israel Julian Grande, a Romanian Jew. They married in London on 29 March 1911; there were no children of the marriage. In 1913 they settled in Bern, Switzerland, anticipating the value of being in 'the Plotting Ground and Listening Post of Europe' during the First World War. Correspondents for British, American and New Zealand newspapers, they also edited the English edition of the International Peace Bureau's journal from 1913 to 1914. Having opposed the South African War (1899–1902) because Britain had previously pledged not to interfere with the liberty and independence of the Boers, Constance Grande was a fervent supporter of the war against German imperialism. She and Julian countered German propaganda by editing a multi-lingual monthly journal and producing pamphlets, in addition to their regular work. They were critical of British pacifists and anti-conscriptionists.
After the war they moved to Geneva, the seat of the League of Nations. The long hours Constance worked had affected her health from 1915, and she was able to attend only two sessions. She maintained, however, that the British Empire was more likely to endure than the league. When she died in Geneva on 16 September 1922, the Christchurch Press commented that her 'grip of facts added to an intimate knowledge of European politics and statesmen…had placed her in the front rank of women journalists'. She had also excelled as a woman mountaineer. A peak in the Southern Alps was named in her honour by Julian Grande in 1923 when on 6 March he made the first ascent of Mt Barnicoat.