Hugh Hamshaw Thomas was born in Wrexham in 1885 and matriculated at Downing College in 1904 studying Natural Sciences. He gained a First Class in Part I before studying History Part II with some aspects of Botany Part II. His interest in Botany was enhanced under Professor of Botany, A. C. Seward (later Master of Downing) and in 1909 he was appointed Curator of the Museum at the Botany School (a position he held until 1923). From 1911-1914 he was Sub-Lector at Trinity, before his election to a Fellowship at Downing in August 1914.

Soon afterwards, with the outbreak of war, he joined the Cheshire Field Artillery and served in France before being sent to Egypt shortly before the Battle of the Somme. In 1916 he transferred to the Royal Flying Corps as Officer in charge of Photography. While with the Palestine Brigade and the Middle East Division he developed the use of aerial photography for intelligence purposes, in particular map making and surveying. (This work was so important that Air Chief Marshal Sir Geoffrey Salmond later commented that the success of General Allenby's campaign was largely due to Captain Thomas's work in this area.) He was twice Mentioned in Despatches, received the Order of the Nile and the Military MBE. After the Armistice, he was sent to India to report on the possibility of an aerial survey of the country and, on returning to Cambridge, assumed the direction of research at the aeronautical department. His Cantor Lectures to the Royal Society of Arts in 1920 described the use of aerial photography in vegetation and forest surveys.

In 1920 Hamshaw Thomas was appointed Dean and Steward of Downing College, positions he held for seven and seventeen years respectively. He was appointed to a University Lectureship in Botany in 1923, the year he married Elizabeth Gertrude Torrance ('Torrie') from Cape Town. The following year, he was awarded the Sedgwick Prize, received the degree of Sc.D. in 1926 and, in 1934, became a Fellow of the Royal Society, in recognition of his work in the field of Palaeobotany and the study of evolution, following a lecture tour of the United States that year.

In 1937 Dr Hamshaw Thomas was appointed Reader in Plant Morphology and he was on an expedition in Jamaica two years later when news reached him of the outbreak of war. On his return, he immediately joined up with the RAF Volunteer Reserve and became involved again with photographic intelligence work. He was closely involved in identifying enemy oil refineries and the location of factories manufacturing V-bombs. He returned to Cambridge in 1943 with the rank of Wing Commander after being mentioned again in despatches.

From 1947 to 1953, Dr Hamshaw Thomas was a member of the Council of the British Association for the Advancement of Science and President of its Botany Section in 1947. For three years, he was also President of the British Society for the History of Science. For twenty-four years, he was Secretary to the International Committee for the Nomenclature of Fossil Plants and was President of the Botanical Section for the 1950 International Botanical Congree. He was President of the Linnean Society of London from 1955 to 1958. During the Darwin and Wallace centenary year in 1958, Dr Hamshaw Thomas was one of twenty international biologists judged to have made the most outstanding contribution to our knowledge of evolution. He received the Linnean Society's Gold Medal two years later. On his retirement from teaching in 1950, he was elected an Honorary Fellowship of Downing College. He died on 30 June 1962.