Joseph Mackrill, surgeon and naturalist, probably studied at Guy's Hospital, London, until 1783, but it is not clear whether he qualified. He may have learned his trade mainly through an apprenticeship. His surviving notebook contains references to countries such as India, Egypt and Turkey, which may indicate that he was at some stage a ship's surgeon. He spent several years in the West Indies and during 1788-1789 was a physician at the military hospital in Trinidad. He moved to Grenada in 1793, and by 1796 was at Garrison Forest, Maryland, United States. That year he published a pamphlet on The history of yellow fever, with the most successful method of treatment (Baltimore, 1796), dealing with the outbreak of a disease described as "yellow fever" in Philadelphia three years earlier and contrasting it with the yellow fever of the West Indies. Around 1801 he became a member of the Medical and Chirurgical Faculty of Maryland and in 1805 moved to Baltimore in the same state. Soon thereafter he came to the Cape Colony, for he was granted a permit to remain in the colony in September 1806 and was admitted to practice as a surgeon by the Supreme Medical Committee of the Cape of Good Hope in August 1807. Though he had also applied to be allowed to practice as an apothecary, he was not licensed as such at this time.
During 1810-1812 Mackrill practiced at 10 Burg Street, Cape Town. In May 1810 he offered a reward to any person who could provide him with cow pox matter. The next year he received a monetary reward of 250 rixdollars from the authorities for bringing vaccine matter against smallpox into the Colony, though he was not the first to do so. W.J. Burchell* visited him in December 1810 to see his collection of natural history specimens, which Burchell described as not very numerous. On 28 December 1811 Mackrill offered his house, furniture, books and preserved birds for sale. The house was sold during 1812. He seems to have been an omnivorous reader with a fairly wide knowledge of chemistry and some schooling in natural history, Latin and philosophy.
In 1814 Mackrill suggested to the Governor, Lord Charles Somerset, that tobacco might be profitably cultivated at the Cape, as its price had risen sharply owing to the War of 1812-1814 between Britain and America. The proposal led to his appointment as the first superintendent of the government experimental farm Somerset, on the southern slopes of the Bosberg (where Somerset East was later established) to grow tobacco and provide forage for the horses of soldiers on the eastern frontier. Here Reverend C.I. Latrobe* visited him in April 1816 and saw much garden produce and many cultivated indigenous plants. The tobacco venture failed when prices fell again after the war, and Mackrill left in November 1816, returning to Cape Town after a trip to the Sneeuwberg. The next year he received 560 rixdollars for plants, bulbs and seeds which he supplied to the government. He left the Cape in 1820 and died of a stroke in England later that year. He was married to Wilhelmina Swarts and left a son.
His notebook, preserved in the Cory Library, Rhodes University, Grahamstown, contains a great deal of miscellaneous information on a variety of topics. Among others he describes a strong earthquake at Cape Town, accompanied by a terrifying noise, on 4 December 1809. Many houses were damaged and some destroyed. Aftershocks continued for some time. The notebook also includes many medical and botanical notes. Mackrill had quite some botanical knowledge, for he always recorded the systematic names of the plants he examined. One of his notes describes how to preserve plants by drying them in hot sand for a day or two. A section of his notebook is devoted to "Medicinal plants of the Cape" and in many cases includes notes on their cultivation or non-medical uses. These descriptions, the first of their kind except for similar notes in C.P. Thunberg's* Travels, have not been published. Some of the material in Dr C.W.L. Pappe's* Flora Capensis medicae prodromus (1850) may have been based on Mackrill's work. The notebook was later in the possession of P. MacOwan*, who added an introductory note in 1888. Mackrill has been credited by the historian G.M. Theal with the introduction of Round-leaved buchu Agathosma betulina as a medicinal herb into England in 1815, and with bringing it to the attention of European medical men. He was man with a keen sense of humour. Some plant specimens collected by him are in the herbarium of the British Natural History Museum.