John Jervis Garrard was educated at Clifton College, Bristol, and King's College, London, and practised as a civil and mining engineer. He was an associate member of the (British) Institution of Civil Engineers. After serving as British vice-consul in Algeria from 1889 to 1892, he came to Natal in May 1893 and remained there for the rest of his life. In 1894 he was appointed as the first justice of the peace for Zululand.
From 1894 Garrard was deputy commissioner and then commissioner of mines for Zululand. In this capacity he wrote a Report on the mining resources of Zululand, issued as a Natal government publication in January 1895. A Map of Zululand showing the relative positions of the various gold and coal fields (London, 1896), on a scale of 5 miles to the inch (1:316 800), was published to accompany this report. Thereafter he produced annually a Report on the mining industry of Zululand for 1895, 1896, and 1897. His post was abolished in 1898, following the incorporation of Zululand into the Colony of Natal during the previous year.
Garrard's interests and expertise included mining law. He compiled Mining law and regulations of Zululand, as in force on 1st January 1897 (Eshowe, 1897), followed by a similar publication for 1907. Meanwhile he served as chairman of the Mining Laws Revision Committee of Natal in 1898. In January 1900 he joined the First Railway Pioneer Regiment as a lieutenant and was on active service during the Anglo-Boer War (1899-1902) until February 1901.
After the war Garrard became consulting engineer to Zululand Collieries. In 1906 he published a paper on "Cheap power: A description of the advantages of suction gas plants" in the Natal Agricultural Journal (Vol. 9, pp. 982-990). In this paper he described an engine driven by coal gas (mostly hydrogen and carbon monoxide). The paper was also published in the form of a pamphlet in Pietermaritzburg. Thereafter his work took him to Swaziland, for in 1914 he published a paper on "The geology of the Swaziland Coalfield" which was published in the Transactions of the Geological Society of South Africa (Vol. 17, pp. 75-84). Three years later his paper on "Hydraulic tin mining in Swaziland" appeared in the South African Mining Journal (No. 1330, 1331, 1333, 1335 and 1338). He became a member of the Geological Society of South Africa in 1905, served on its council from 1910 to 1920, and was elected president of the society for 1919.