Mary R.H. Thomson received her secondary schooling at the Good Hope Seminary in Cape Town and passed the matriculation examination of the University of the Cape of Good Hope in 1912. She continued her studies at the South African College (which later became the University of Cape Town) and was awarded the Bachelor of Arts (BA) degree with honours in botany by the University of the Cape of Good Hope in 1915. In collaboration with Professor H.H.W. Pearson*, head of the Department of Botany at the South African College, she published a paper, 'On some stages in the life history of Gnetum' in the Transactions of the Royal Society of South Africa (1917, Vol. 6, pp. 231-270).
In 1919 Thomson was appointed in the Division of Plant Pathology and Mycology of the Department of Agriculture in Pretoria, under Mr Illtyd B. Pole-Evans*. They were married in 1922, and had two children. From this time Mary published under her married name. As co-author to her husband she published a paper on 'Rise in temperature of living plant tissue when infected by parasitic fungus' (Nature, 1922, Vol. 110, pp. 480-481). The next year she produced two papers on rusts in South Africa: 'A sketch of the life-cycle of the rust on Besem Grass and wild Sweet Pea' (Department of Agriculture, Science Bulletin No. 1, 1923) and 'A sketch of the life-cycle of the rust on mealie and Oxalis' (Ibid, No. 2, 1923).
In 1955 Pole-Evans settled in Umtali, Southern Rhodesia (now Mutare, Zimbabwe), where her husband died in 1968. She remained there for the rest of her life.