John Ray Cowell served an apprenticeship in the Ipswich works of Messrs E.R. and F. Turner from 1881 to 1885. After further experience as a marine engine fitter he went to sea in 1886 as an engineer in vessels of the Monarch Line. By 1892 he had risen to chief engineer and had acquired an Extra First-Class Board of Trade Certificate. He then joined Messrs Turner as a draughtsman in their London Office, but soon became a partner to a consulting engineer in London. He became an associate member (1893) and later a member (1897) of the (British) Institution of Mechanical Engineers and was also a member of the Institution of Electrical Engineers.
Cowell came to the Transvaal in 1894 and for a brief period was assistant manager at the Austral Iron Works in Johannesburg. In April the next year a Town Lighting Department was established in Johannesburg and he was appointed its first engineer and general manager, a post he held to 1902. Both gas and electricity were supplied by his department. In 1895 a total of 117 houses were connected to the electricity supply and two years later this number had grown to 370.
Cowell became a member of the South African Association of Engineers and Architects in June 1895, and served on its council during 1898/1899. At a meeting on 28 July 1897 he read a paper on "Carburetted water gas", dealing with its generation and use for lighting and other industrial purposes. The process he described generated gas from the action of steam on coke, producing roughly equal parts of hydrogen and carbon monoxide, which was then reacted with heated oil vapour to form some hydrocarbons. Gas generation in Johannesburg started in 1892.
Cowell also joined the Mechanical Engineers' Association of the Witwatersrand (founded in May 1898) before the end of 1898. In "Notes on internal combustion engines for mining operations", published in the association's Journal (1902-1903, Vol. 1 (3), pp. 40-44) he reported on experiments with a 500 horsepower gas engine. This association became the Transvaal Institute of Mechanical Engineers in 1905. Cowell was a member of its council from 1905 to 1909 and contributed a paper on "Condensing plants" to its Journal (1909/10, Vol. 8). In 1905 he became a member also of the British Association for the Advancement of Science, when it visited South Africa for joint meetings with its South African counterpart.
In 1902 Cowell resigned his post to join the Johannesburg engineering firm Blanc & Co, where he became managing director for the rest of his career. He was married to Sarah Louisa Emma Porter, who died in 1925.