Norman Douglas Simpson was born in Carlton Miniott, near Thirsk in the North Riding of Yorkshire on 23 September 1890, the son of a vicar, Reverend James Douglas Simpson (died 1936) and Elizabeth Saunders of Airy Hill, Whitby, Yorkshire, who was the daughter of a wealthy landowner, Charles Saunders. Simpson was encouraged by his father who had an interest in botany and began to form his Herbarium of British plants in 1903, aged 12. He attended Aysgarth School in Yorkshire and became friends with the Foggitt family who were also keen botanists and it was William Foggitt (c.1835-1917) and others who founded the Botanical Exchange Club which later became the Botanical Society of the British Isles of which Simpson became a life-long member.
In 1904, Simpson attended Clifton College, Bristol, and in 1908 he went to Trinity College, Cambridge (his father's college) and read Botany and Zoology graduating BA with a third in Natural Sciences Tripos in 1911. By this time Simpson had a Herbarium of over 1,400 species and varieties and he had become an expert Microscopist and was made Fellow of the Royal Microscopical Society in 1912. He remained a member until his death. He was keen to take a position at Kew Herbarium but they had no post to offer him. However, Assistant Director A W Hill suggested he might undertake the identification of specimens collected the previous year in North-Western Mongolia and Chinese Dzungaria by Morgan Philips Price (c.1885-1973). In November 1911 Morgan agreed to pay Simpson 30/- a week for six months to identify and list his plants with a view to publication. Simpson worked on this with the help of Otto Stapf (c.1857-1933) until 1912 and it also led him into studying the genus Astragalus. Simpson's resulting enumeration was submitted to the Linnean Society by Stapf and was published in October 1913 and included new species.
He returned to college and gained a Cambridge Diploma in Agricultural Studies in 1914. Simpson was a keen mechanic, motorcyclist and motorist and in 1915 he joined the Red Cross as a motorcyclist and was sent to the Hospital at Poperinghe in Belgium. In November 1915 he enlisted in the Army Transport Corps and rose through the ranks being promoted to Captain and served until 1920 when he was discharged.
After the war, Simpson went to live with his father at 'Maesbury' in Bournemouth, who had retired in 1916 and moved to Bournemouth from Yorkshire as he had family there and after his father's death Simpson lived at 'Maesbury' until his death. Simpson would have liked a post at Kew but there were none available. In February 1921, he joined the staff at the Cotton Research Board's Sections at El Giza where he became an Economic Botanist. In the November of 1921, he started the Botanical Section's Herbarium and when he left Egypt in 1930 it had grown to 8,450 specimens and many were duplicated in his own Herbarium. His Cotton (Gossypium) collection was presented to Sir George Watt (c.1851-1930) which is now at Edinburgh and another set was presented to Kew. In 1926, Simpson moved to the Irrigation Services, Ministry of Public Works, Egypt and was partly employed in the Sudan where he became knowledgeable in water plants. His contract expired in 1930 and was not renewed and he returned to England via travelling through Europe. In September 1930, the Colonial Office offered him a job as Systematic Botanist in the Agricultural Department at the Peradeniya Botanic Garden, Ceylon, on a wage of £720 per annum and a pension. In bought his beloved car, the Alvis 12/50 for £395 which he took to Ceylon and was still driving his car until his death in 1973. The post ended abruptly in 1932 as they abolished his post and he returned to England in September 1932 via the Far East, Japan and the United States of America.
Simpson then settled at 'Maesbury' and as his family were wealthy, he never sought paid work again. He spent his time collecting, indexing and arranging his Herbarium. He travelling much in order to collect specimens and map the flora of various countries, such as Morocco, Algeria, Tunisia (Simpson had a knowledge of Arabic), Ireland (where he botanised Ireland with various others) and Jordan - all in his Alvis car which had a plant press in the boot. Simpson added many new species to his Herbarium. He also spent much of his retirement collecting books and assembled a large and comprehensive botanical library. He also collected works by Richard Burton, John Buchan, T E Lawrence and books relating to North Africa and the Near East which sold at auction after his death for £13,077. Simpson published little himself. In 1960, he published at his own cost of £2,000 his index A Bibliographical Index of the British Flora which started to be compiled in 1941 and provided an invaluable compilation of classified referencing to books and articles in periodicals relating to the flora of the British Isles.
Simpson died on 29 August 1974, just short of his 84th birthday from a heart condition. On the death his Herbarium included 5,800 sheets from Egypt, 1,580 from the Sudan, 400 from Jordan, 600 from Morocco, 800 from Algeria, 500 from Tunisia, 600 from Cirenaica, 18,100 of British and Irish plants and 1,300 of Continental European plants which he collected from 1903-1973. The Sudan, Egypt and Jordan collections were deposited to The Royal Botanical Gardens, Kew and the rest to the Natural History Museum. His main collections of botanical books were presented to the Botany School at Cambridge, The Natural History Museum, Royal Botanical Gardens, Kew and Reading University.