Helen Flora Victoria Scales was born in Lower Hutt on 24 May 1887. She was the daughter of Gertrude Maynard Snow and her husband, George Herbert Scales, an insurance agent and the founder of the exporters and auctioneers G. H. Scales and Company. Flora attended school in Lower Hutt, then a private school in Thorndon. She showed an obvious talent for drawing, and at the age of 16 was sent to Christchurch to board at Mrs Croasdaile Bowen's school and attend the Canterbury College School of Art part time for two years.
In 1906 and 1907 Flora Scales exhibited in the annual exhibitions of the New Zealand Academy of Fine Arts. The following year she travelled to England to enrol at Frank Calderon's school of animal painting. Her four years' study there concluded with the hanging of her oil Cattle mustering in New Zealand in the summer exhibition of the Royal Academy of Arts in 1911.
After her return to New Zealand Scales joined the Academy Studio Club in 1914, broadening her artistic concerns beyond Calderon's academic approach by painting outdoors, and gaining a considerable reputation for her work. Her studies, which included etching with James MacDonald, continued during the First World War when, as a member of the Voluntary Aid Detachment of the Red Cross, she worked at the Taumaru Military Convalescent Hospital, Lowry Bay.
When her parents separated, Flora Scales and her mother and sister unsuccessfully tried to make a living as orchardists in Nelson. George Scales died in 1928, leaving Flora a legacy which allowed her to devote all her time to art. Ambitious for knowledge, she went to Paris. Stimulated by the public art collections but dissatisfied with her sessions at the Académie de la Grande Chaumière, Scales went to Hans Hofmann's school of art in Munich. Over the winter of 1931–32 she studied Hofmann's principles of modernism with Edmund Kinzinger. The lectures illustrated the theory that painting should be autonomous, without dependence on naturalistic perspective or representation.
When Scales returned to New Zealand in 1934 this aspect of her painting was a revelation to Toss Woollaston, to whom she gave some valued instruction. He found her dignified, shy and single-minded, noting that 'Her attitude seems to be that to draw and paint is better than to discuss drawing and painting.'
Apart from Woollaston, W. H. Allen and Frederick Page, few in New Zealand understood the modernism of the work Scales exhibited. In late 1935 or early 1936, discouraged by the isolation of her position, she returned to paint in England and France. She attended Roger Bissière's lectures at the Académie Ranson and enrolled at the Heatherley School of Fine Art in 1959, but these were brief episodes in a career that from 1932 was conducted entirely in the spirit of independent enquiry into purely pictorial problems.
Her painting was interrupted by the Second World War, during which she was interned for two years in France. Some of her work was lost during this period. Following the war she lived in England with her mother, sister and niece. When she resumed work in the 1950s, Scales's handling of paint became more confident, with broader brush-strokes, and the effects – particularly in the two series based on the boarding-house in Cornwall and the orchard at Bry-sur-Marne – increasingly atmospheric and visionary.
In 1972 Flora Scales resettled in New Zealand, and in 1975 her first public solo exhibition was arranged by Colin McCahon and the Auckland City Art Gallery. She returned to France in 1976, but a heart attack the following year brought her back. After a short period in Auckland, she moved to a retirement village in Rotorua. She never married, and died on 11 January 1985 at Rotorua Hospital.
Flora Scales was dedicated to painting. She was rarely satisfied with her work and for this reason never approached a dealer. She painted mainly small, almost abstract landscapes, portraits and flower studies. Humble, unambitious and seemingly self-sufficent, she nevertheless had considerable influence on New Zealand painting, less through her own work than through that of Toss Woollaston. Her paintings show her as an artist of profound integrity. Out of her passion for the process of creation she developed her art according to the most rigorous concepts of modernism. A large proportion of her work is in private ownership in New Zealand; the Alexander Turnbull Library holds her papers and the main public collection of her paintings.