Archibald Campbell MacDonald was educated at the Royal Agricultural College at Cirencester, England, and acquired four years experience as an estate manager before he arrived at the Cape of Good Hope in August 1889 to take up a position as agricultural assistant in the civil service of the colony. He was also appointed principal and tutor at the Government Agricultural School that was being established in Grahamstown. Its courses were to include subjects such as chemistry, botany and geology for agriculture. He held this second appointment for a short period only.
During the next two years MacDonald regularly contributed articles and notes to the Agricultural Journal of the Cape of Good Hope, for example: "Rotation of crops" (1890, Vol. 3, pp. 26-27) and "Experiments with ensilage" (1890, Vol. 3, pp. 110-112), the latter describing small scale experiments conducted by him and some farmers. In July 1891 he was sent to Graaff-Reinet to report on measures to eradicate prickly pear and demonstrated how the plants could be destroyed with an "arsenical scrub exterminator". His report, "Prickly pear in South Africa", was submitted to a select committee of the House of Assembly and published in the Agricultural Journal (1891, Vol. 4, pp. 21-25).
In 1893 the Department of Agriculture of the Cape Colony published a number of substantial pamphlets on various aspects of agriculture. Several of these were compiled by MacDonald, namely Dairy breeds (58 pp.), The dairy industry in Great Britain (20 pp.), Ensilage, or, the preservation of green fodder (34 pp.), and Tomatoes and fruit for export (8 pp.). Within the next two years he was sent on a dairy mission to Australia, with the additional instruction to bring back various species of ladybirds to serve as breeding stocks in an effort to control scale insects and aphids at the Cape. With the help of Claude Fuller*, then assistant entomologist in New South Wales, he collected large numbers of four species and handed them over to the newly appointed Government Entomologist Charles P. Lounsbury*, but on release they all died out.
During 1892-1895 MacDonald regularly heald lectures on dairying, with a travelling dairy. He also conducted some crop and pasture research, for example, in 1897 he imported numerous varieties of wheat from New South Wales, Australia, and tested them for rust resistance and yield. The results were published in the Agricultural Journal of the Cape of Good Hope (1897, Vol. 11, No. 2) as "Wheat experiments in the Colony". The best varieties, both as regards rust resistance and yield, became the standard varieties at the Cape for the next two decades.
In July 1899 MacDonald chaired a meeting of fruit exporters in Cape Town at which the Western Province Fruit Exporters' Association was founded. The next year he attended a fruit-growers' congress in Stellenbosch. That year, during the Anglo-Boer War (1899-1902), he appears to have been transferred to the newly created Orange River Colony (now the Free State). After the war, on 1 October 1903, he was appointed assistant director of the Department of Agriculture in the Transvaal Colony, under F.B. Smith*. He retired on pension in 1907 and then became director of agriculture of British East Africa (now Kenya), stationed in Nairobi. In that capacity he visited South Africa in 1917 to buy stock. He also published a paper on "Leaf blight - a fungal disease of coffee" (Bulletin, Kenya Department of Agriculture, 1912.