Henry James Johnston-Lavis was born on July 19, 1856, in London, England, the son of Frances Lavis (1827–1880), an artist.

He was a vulcanologist and physician. His interest in geology was sparked at the grammar school, Iver, Buckinghamshire. For the benefit of his mother's health, the family moved to Marseilles, France, where he began medical training. In 1873, he transferred to University College, London. Here he was inspired by the teaching of the influential geologist John Morris, and at the age of nineteen, he was elected a Fellow of the Geological Society. His first paper on the Triassic strata at Sidmouth was published in 1876. Some bones he had discovered were found to be a new species of amphibian and were named Labyrinthodon lavisi in his honour. He qualified as MRCS, LRCP, and LSA in 1878. He entered medical practice in Stalbridge, Dorset, and then moved to Plaistow, before gaining the degree of B.Sc. in Paris. In 1879, he moved to Naples, Italy, where he started a medical practice for English-speaking communities, acquiring the degree of M.D. in Naples in 1884. In Italy, he was able to pursue his geological interests. He published a monograph (1885) on the earthquakes that occurred at Ischia in 1881 and 1883. He devoted much of his spare time to the study of Monte Somma and Vesuvius, presenting a paper on the subject to the Geological Society in 1884. In 1891, he published a scientifically accurate geological map of Vesuvius, representing the first detailed geological map of the area. In 1892, he was appointed Professor of Vulcanology at the Royal University of Naples. In 1894, he moved to the south of France, qualifying in medicine again at the University of Lyons in 1895. He held the position of English consulting physician to the Établissement de la Société Générale des Eaux Minérals de Vittel. He acquired a magnificent collection of books, lithographs, gouaches, engravings, photographs, and geological specimens, which he offered to the geology museum at University College, London, in 1913.

In 1879, he married Antonia Francoise Bourdariet de St. Aupre (–1917). He died on September 10, 1914, in a car accident near Bourges, Cher, France.