Joseph Lunt was educated at Owen's College, Manchester, where he obtained the Bachelor of Science (BSc) degree. As co-author with H.E. Roscoe he wrote a textbook, Inorganic chemistry for beginners (New York, 1893). An early paper by him dealt with "Stellar photography with small telescopes without driving clocks" (Nature, 1896). At this time he was a member of the British Astronomical Association and early in 1897 headed its Photographic Section. In July 1897 he was appointed as an assistant at the Royal Observatory, Cape of Good Hope, directed by Dr David Gill*. He arrived for duty in October that year and remained in his post until his retirement in 1926.
From 1900 to 1903 Lunt spent part of his time working with R.T.A. Innes* to obtain a valuable series of double star measurements with the Victoria telescope. During 1902 he went on a visit to England. However, most of his time was spent in spectroscopic work. This involved studying the spectra of various elements in the laboratory, and using the Victoria telescope to photograph faint and peculiar stellar spectra. He also searched for, and found, some star-like nebula (described in a paper with Innes in 1902), and used the spectroscope to determine the radial velocities of stars. In addition to his papers in British astronomical journals, much of his spectroscopic work was published in Volume 10 of the Annals of the Cape Observatory, issued in separate parts at various times. For example, "The spectra of silicon, fluorine and oxygen" (Part 2, 1906), "On the spectra of graphites and 'lead pencils' and on a convenient comparison spectrum" (Part 4, 1913), "The radial velocities of 120 southern stars observed at the Cape" (Part 5, 1921), "On the variable orbit of the spectroscopic binary, 42 Capricorni" (Part 6, 1921), and "On the orbits of the seven spectroscopic binary stars..." (Part 7, 1924). Around 1905 he discovered evidence of the presence of the element europium in the spectra of the stars alpha Bootis and beta Geminorum and published his findings in the Proceedings of the Royal Society of London. In September 1914 he independently discovered a comet in the constellation Dorado, but was not the first to observe it. That same year he published a paper "On the spark spectrum of the N'Kandhla meteorite" in the Report of the South African Association for the Advancement of Science (pp. 243-244). Later papers by him in the South African Journal of Science dealt with "Stellar distances, magnitudes and movements" (1921, Vol. 18, pp. 32-47) and the spectrographic analysis of the newly discovered Germanium-Gallium mineral Germanite (1923, Vol. 20, pp. 157-165).
By 1902 Lunt was a Fellow of the Royal Astronomical Society, the Institute of Chemistry (London), and the Chemical Society. That year he became a foundation member of the South African Association for the Advancement of Science and later served as a member of its council, as joint secretary of section A (which included astronomy) in 1919, and as president of that section in 1929. During 1900-1903 he was an examiner in undergraduate chemistry and metallurgy, and in 1901 in chemistry at the MA level, for the University of the Cape of Good Hope. In 1909 he was awarded the degree Doctor of Science (DSc) by Victoria University, Manchester, and as a result was admitted to the same degree by the University of the Cape of Good Hope. When the Cape Astronomical Association was founded in December 1912 he was elected joint vice-president. After a period of two years during which the association was inactive owing to the effects of World War I (1914-1918) he was elected an honorary vice-president in 1916, and president from 1917 to 1919. At this time he designed an equatorial sundial which was constructed by Mr T.R. Miller, mechanic to the Royal Obsevatory, and erected at the Castle in Cape Town. Lunt described it in the fifth Circular of the Cape Astronomical Association. His hobbies were agriculture, gardening, and later entomology. After his retirement he lived in Kenilworth, Cape Town. He was married and died of hear disease.