William Roxburgh studied botany at Edinburgh and then obtained a position as surgeon's mate on a ship of the (English) East India Company in 1766. After several voyages to India he completed his medical studies at Edinburgh. In 1776 he was appointed assistant surgeon in the company's medical establishment at Madras (now Chennai, India), becoming a full surgeon in 1780. The next year he was stationed at Samucotta, some 320 km north of Madras. He met the plant collector Johan G. König*, collected plants himself, and cultivated many useful species. In 1793 he was appointed botanist in the Carnatic (the region around Madras) and superintendent of the company's Calcutta (now Kolkata) Botanic Garden, a position he held until 1813. He was a competent manager of the garden and a pioneer in the study of the flora of India. The Society of Arts awarded him its gold medal no less than three times for his research on Indian plant fibres. He was elected a Fellow of the Linnaean Society (FLS) in 1799.
After visiting England for health reasons from December 1797, Roxburgh stayed at the Cape from 1798 to October 1799, accompanied by his wife (he was married three times and had about 12 children) and his son John Roxburgh*. While at the Cape William collected plants to take to India. According to Lady Anne Barnard (1999), who met him frequently between early February and the end of June 1799, he did not collect very far into the interior, but exchanged plants with others who had done so. He also received many plants from gardeners and collectors in Cape Town. At this time he was fit enough to climb Table Mountain, where he found a great variety of seeds. According to Robert Brown* he appears to have given special attention to the family Proteaceae, discovering several new species and making observations on the sexes, sizes and locations of these plants.
During 1805-1808 Roxburgh again had to return to Britain for health reasons. In 1813 his health finally broke down and he retired. On his final return to England in 1814 he visited the Cape again and then spent six months on the island St Helena.
Most of Roxburgh's published papers (in Asiatic Researches and the Philosophical Magazine) were descriptions of new plant species, particularly plants and trees of possible economic importance. When he left India he had completed the manuscript of a book, Hortus Bengalensis, or a catalogue of the plants grown in the Honourable East India company's botanic garden at Calcutta. It contained a list of 1510 species cultivated in the garden and was published in Serampore in 1814. He had also written his most important work, Flora Indica by this time. After much delay the first two volumes, including additional material by W. Carey and N. Wallich*, were published in Serampore in 1820 and 1824 respectively, with a three volume edition following in 1832. The book was particularly important for the economic botany of India.
Roxburgh apparently did not keep a personal plant collection. He presented most of his specimens to Sir Joseph Banks* (these are now in the Natural History Museum, London), the Linnaean Society (now also in the Natural History Museum), and A.B. Lambert of London (now in the Conservatoire et Jardin botaniques, Genčve, Switzerland). Over the years he accumulated a valuable collection of more than 2500 flower paintings by Indian artists. One set of these is at Kew Gardens and a second set in the Natural History Museum and the Central National Herbarium, Kolkata, India. A selection of 300 of the paintings, with Roxburgh's descriptions of the plants, was published as Plants of the coast of Coromandel (3 vols, 1795-1819).