Smythies was born in India, to E. A. Smythies, silviculturist of Uttar Pradesh and, in the 1940s, Chief Conservator of Forest of Nepal, and his wife, Olive, well-known author of The Tiger Lady. After school in the UK, Bill read botany and forestry at Balliol College, Oxford.
Bill's grandfather came to India in 1873 to join the Indian Forest Service and served until 1902 around Dehra Dun. His father had degrees in forestry and geology from Oxford and served in the Indian Forest Service from 1908 to 1940. He was based in Nainital, where Bill was born in 1912. He wrote: ... "started hill trekking at the age of six months, camping in tents in the hills of Kumaon... brought up within sight of Nanda Devi and Trisul - who could fail to have a love of mountains and natural history?"
Smythies father took up a contract post of Forest Advisor to the Maharaja of Nepal and moved to Kathmandu after 1940 and stayed on till 1947. During this time Bill used to visit his father in Nepal and had access to places that were normally out of bounds for foreigners. Bill Smythies joined the Burma Forest Service in 1934 and during this time he explored the botany and ornithology of these Burmese regions with his Kachin guide and friend Sumdu Mai. He spoke fluent Burmese, Jingpo, Malay and Iban. He was a great fan of the British botanist and explorer Kingdon-Ward.
In January 1949 he was appointed to the Colonial Forest Service in Sarawak where he spent 15 years. At the age of 52, the day he left Sarawak, he married Florence "Jill" Mary who was a talented botanical artist. The next fifteen years were spent in the Spanish Sierras, the mountains of Britain, the Alps and the Pyrenees before moving to England. Jill died in 1994. In 1986, in honour of his wife, he established an annual Jill Smythies Award through the Linnean Society of London "for publishing illustration, such as drawings or painting, in aid of plant identification, with the emphasis on botanical accuracy and accurate portrayal of diagnostic characteristics. Illustrations of cultivars of garden origin are not eligible".
He wrote several major books and papers including
- The Birds of Burma (first published 1940)
- Birds of Borneo
- Common Sarawak Trees
- Flowers of South-West Europe (with Oleg Polunin and Jill Smythies)
- Flowers of Greece
- Flora of Spain and the Balearic Islands. Englera 3: 1 – 88 (1984)
- Gathorne Cranbrook (22 October 2011). "Obituary: Bertram E. Smythies". The Independent.
- Eric Pace (2 August 1999). "Bertram Smythies, 86, a Writer On Birds of Burma and Borneo". The New York Times.
- Davison, G.W.H. (1999). B.E. Smythies. (In: Smythies, B.E.; & Davison, G.W.H. The Birds of Borneo. 4th edition. Natural History Publications (Borneo): Kota Kinabalu). ISBN 983-812-028-6
- Wright, Belinda.(1999). Obituary: Bertram 'Bill' Smythies. OBC Bulletin 30 (Nov 1999): 7-8.