Mary Armour studied Drawing and Painting at The Glasgow School of Art from 1920. In 1925, after a post-diploma year and teacher training, she became an art teacher, and in 1927 she married the landscape and figure painter William Armour (1903–1979).
Armour exhibited at a number of prestigious institutions from the 1930s onwards, including the Royal Academy, Royal Scottish Academy, Royal Scottish Society of Painters in Watercolour, Scottish Society of Artists, and Glasgow Institute of the Fine Arts. She was awarded the Guthrie prize at the Royal Scottish Academy in 1937, and in 1941 she was elected an associate at the Academy. In addition to her art practice, Armour was a lecturer in still-life painting at the GSA from 1951 – 1961.
Awards and honours included full membership of the Royal Scottish Academy in 1958, the Cargill prize at the RGIFA in 1972, full membership of the RFIFA in 1977, and an honorary Doctorate from Glasgow University in 1982. In later life she was elected honorary president of both the GSA and the RGIFA.