Joseph Lewis became a student at the South African College, Cape Town, in 1889 and matriculated through the University of the Cape of Good Hope in 1890. Continuing his studies he won a gold medal for science in 1892 and graduated as Bachelor of Arts (BA) with honours in mathematics and natural science in 1894. The degree was awarded by the University of the Cape of Good Hope. From 1899 to the end of the Anglo-Boer War (1899-1902) he worked in a a variety of temporary positions that reflect the unsettled times, but also demonstrate his versatility. The South African College employed him as teacher of matriculation mathematics (1899); assistant in mathematics (1901-May 1902); stand-in for W.J.A.E. Horne* of the Physics Department, who had been called up for active duty (1900); and stand-in for the professor of Chemistry, P.D. Hahn*, who was on leave in Europe (July-September 1900). At the Diocesan College, Rondebosch (Cape Town) he served as temporary lecturer in chemistry and mathematics at times during 1898-1901. The Government Analytical Laboratory in Cape Town employed him as temporary government analyst (last half of 1899), and as stand-in for analyst J.G. Rose*, who was not yet back from war duty (1901). Eventually, in May 1902, he obtained a permanent appointment as government analyst at the Government Analytical Laboratory under C.F. Juritz*, who valued his work highly. That same year he was furthermore awarded the degree Master of Arts (MA) by the University of Cambridge. In 1904 he married Ethelreda Howe, who arrived from Britain for that purpose and became a well-known author of English fiction in South Africa.
During 1906 Lewis took charge of the Government Laboratory in Grahamstown for six months, in the absence of J. Muller*, who was in Europe owing to illness. At this time he served as an examiner in chemistry and metallurgy for the University of the Cape of Good Hope. During the last half of 1909 he helped out as temporary lecturer in chemistry at the School of Agriculture at Elsenburg, near Stellenbosch. By this time he had developed a serious interest in the chemical foundations of viticulture and the wine industry. An article by him on "Some analyses of Cape wines", based on a paper delivered to the Cape Chemical Society on 30 August 1907, was published in the Agricultural Journal of the Cape Colony (Vol. 31(3), pp. 292-294). It consisted mainly of tables of results. A later contribution to the same journal (February 1910), dealing with the rate of brandy distillation, was also based on a paper read before the Cape Chemical Society. In 1910 he was awarded the degree Doctor of Science (DSc) by the University of the Cape of Good Hope for a thesis titled Contribution to the study of the development of the grape, and the changes in grape-must produced by alcoholic fermentation [grape-must is grape juice before fermentation is complete].
Lewis was appointed senior chemist in charge of the Grahamstown Analytical Laboratory in 1911, and in April the next year, following the formation of the Union of South Africa in 1910, became an assistant government analyst. During 1911-1912 he wrote some articles relating to agricultural chemistry for the Agricultural Journal of the Union of South Africa. By 1922 he worked in the Government Laboratory in Johannesburg. He published three papers in the Journal of the South African Chemical Institute at this time, on hydrocyanic acid and novatophan (1921), on arsenic (1923), and on acocantherine (1925).
He became a member of the South African Association for the Advancement of Science before the end of 1903, but only for a few years. He became a foundation member of the South African Association of Analytical Chemists (from 1921 the South African Chemical Institute) in 1912, served on its council from 1918, and as president for 1920/1.