He was the eldest child of a Tewkesbury head teacher and the elder brother of Raymond Priestley, the British geologist and Antarctic explorer.

In 1911, he married Marion Ethel Young at Bristol, and in the same year, he was appointed professor of botany at the University of Leeds.

He was the first warden to the male students at Leeds and organised many social activities, including a staff dancing class and "botanical parties".

[4][a] He was the eldest child of eight children of Joseph Edward Priestlay, then head teacher of the school, and Henrietta, née Rice.

[6]: 10 In 1875, Priestley's father graduated from the University of London with a second class Bachelor of Arts degree in animal physiology.

[13] Donald was a commercial traveller working for their mother's family firm, William Rice and Company, corn millers and seed merchants at Tewkesbury.

[16] Joyce married Herbert William Merrell, who served with the Gloucester Regiment in World War I,[17] and in later life, was an accountant on the staff of the University of Leeds.

[21] In July 1898, he passed an elementary examination in Pitman shorthand,[22] before taking a physical geography course at the Science Hall on Oldbury Road, Tewkesbury.

[26] Though primarily a botany student, Priestley took courses in chemistry and physics at Bristol,[27] and in August 1901, he gained a first class pass in the University of London intermediate science examination.

[32] In the same month, he was awarded a probationary bursary worth seventy pounds, by the Commissioners for the Exhibition of 1851,[33] to study the cell biology of rust fungi.

[39] In 1906, he published a paper with Francis Usher, later a reader in colloid chemistry at the University of Leeds,[40] that postulated that chlorophyll in vitro is reduced to formaldehyde in the presence of carbon dioxide and light.

[41]: 53  Vernon Herbert Blackman, professor of botany at the University of Leeds whom Priestley would succeed in 1911,[41]: 51  considered the evidence unsatisfactory.

[41]: 54 In 1908, the college received a grant of fifty pounds from the Board of Agriculture to enable the biology department to conduct research on the effect of electricity on plants.

[44] He noted that young wheat leaves from electrified plots were, "in the opinion of many observers, darker green than the control plants.

"[45]: 180  He suggested that the darker green could result from a continuous amount of nitrates being added to the soil, in a similar manner to the oxidation of atmospheric nitrogen by lightning.

[49] In 1910, he was appointed consulting botanist to the Bath and West and Southern Counties Society,[50] after William Carruthers had resigned in the previous year.

[51] In 1911, Priestley was appointed professor of botany at the University of Leeds,[52] succeeding Blackman, who had left to join the Institute of Vegetable Physiology at Imperial College London.

He had been in command of the University Officers' Training Corps at both Bristol and Leeds, and on 9 August 1914, he was sent to France with the British Expeditionary Force.

[52] He had been influenced by the work of Albert Frey-Wyssling on cell walls and William Henry Lang's research on plant morphology and anatomy.

[62] In 1929, he and Lorna I. Scott, co-author of Priestley's textbook An Introduction to Botany,[63] attended the association's meeting in South Africa,[64] based at the universities of Cape Town and Witwatersrand, Johannesburg.

They stopped at Saint Helena, in the South Atlantic Ocean, to the west of south-western Africa,[66] where they collected a number of bryophyte specimens.

[72] In 1941, the senate appointed Priestley as pro-vice-chancellor for a second term, after Bernard Mouat Jones, then vice-chancellor, had left the University in February to complete National Service.

[73]: 111 Priestley married Marion Ethel Young before leaving Bristol to take up his appointment as professor of botany at the University of Leeds.

[82] Michael Cullen, Phyllis Mary's son and Priestley's grandson,[83] is a former senior research fellow at the Met Office and visiting professor in mathematics at the University of Reading.

[95] He died after a long illness at his home in Weetwood, Leeds, on 31 October 1944, and the funeral was held at Lawnswood crematorium in the morning on 3 November 1944.

[39][96] A large number of university staff attended including Mouat Jones, Bonamy Dobrée, and Arthur Stanley Turberville.

[63] After Priestley's death, a memorial trust fund was established to provide grants to botany students at the University of Leeds.