James Prinsep FRS (20 August 1799 – 22 April 1840) was an English scholar, orientalist and antiquary. He was the founding editor of the Journal of the Asiatic Society of Bengal and is best remembered for deciphering the Kharosthi and Brahmi scripts of ancient India. He studied, documented and illustrated many aspects of numismatics, metallurgy, meteorology apart from pursuing his career in India as an assay master at the mint in Benares.

James Prinsep was the seventh son and the tenth child of John Prinsep (1746–1830) and his wife, Sophia Elizabeth Auriol (1760–1850). John Prinsep went to India in 1771 with almost no money and became a successful indigo planter. He returned to England in 1787 with a fortune of £40,000 and established himself as an East India merchant. He moved to Clifton in 1809 after incurring losses. His connections helped him find work for all his sons and several members of the Prinsep family rose to high positions in India. John Prinsep later became a member of parliament. James initially went to study in a school in Clifton run by a Mr. Bullock but learnt more at home from his older siblings. He showed a talent for detailed drawing and mechanical invention and this made him study architecture under the gifted but eccentric Augustus Pugin. His eyesight however declined due to an infection and he was unable to take up architecture as a profession. His father knew of an opening in the assay department at the mint in India and sent him to train in chemistry at Guy's Hospital and later as an apprentice to Robert Bingley, assay master at the Royal Mint in London (1818–19).

Prinsep found a position as an assay master at the Calcutta mint and reached Calcutta along with his brother Henry Thoby on 15 September 1819. Within a year at Calcutta, he was sent by his superior, the eminent orientalist Horace Hayman Wilson, to work as assay master at the Benares mint. He stayed at Benares until the closure of that mint in 1830. He then moved back to Calcutta as deputy assay master, and when Wilson resigned in 1832, he was made assay master (overruling Wilson's nominee for that position, James Atkinson) at the new silver mint designed in Greek revival style by Major W. N. Forbes.

His work as assay master led him to conduct many scientific studies. He worked on means for measuring high temperatures in furnaces accurately. The publication of his technique in the Philosophical Transactions of the Royal Society of London in 1828 led to his election as a Fellow of the Royal Society. He suggested the possibility of visual pyrometric measurement using a calibrated series of mica plates as well as using the thermal expansion of platinum but considered that a practical approach was to use calibrated combinations of platinum, gold and silver alloys placed in a cupel or crucible and observe their melting. He also described a pyrometer that measured the expansion of a small amount of air held within a gold bulb. In 1833 he called for reforms to Indian weights and measures and advocated a uniform coinage based on the new silver rupee of the East India Company. He also devised a balance so sensitive as to measure three-thousandth of a grain (≈0.19 mg).

James Prinsep continued to take an interest in architecture at Benares. Regaining his eyesight, he studied and illustrated temple architecture, designed the new mint building at Benares as well as a church. In 1822 he conducted a survey of Benares and produced an accurate map at the scale of 8 inches to a mile. This map was lithographed in England. He also painted a series of watercolours of monuments and festivities in Benares which were sent to London in 1829 and published between 1830 and 1834 as Benares Illustrated, in a Series of Drawings. He helped design an arched tunnel to drain stagnant lakes and improve the sanitation of the densely populated areas of Benares and built a stone bridge over the Karamansa river. He helped restore the minarets of Aurangzeb which were in a state of collapse. When he moved to Calcutta, he offered to help complete a canal that had been planned by his brother Thomas but left incomplete by the latter's death in 1830. Thomas's canal linked the River Hooghly with branches of the Ganges further to the east.

In 1829, Captain James D. Herbert started a serial called Gleanings in Science. Captain Herbert, however, was posted as Astronomer to the King of Oudh in 1830, leaving the journal to the editorship of James Prinsep, who was himself the primary contributor to it. In 1832 he succeeded H. H. Wilson as secretary of the Asiatic Society of Bengal and suggested that the Society should take over Gleanings in Science and produce the Journal of the Asiatic Society. Prinsep became the founding editor of this journal and contributed articles on chemistry, mineralogy, numismatics and on the study of Indian antiquities. He was also very interested in meteorology and the tabulation of observations and the analysis of weather data from across the country. He worked on the calibration of instruments to measure humidity and atmospheric pressure. He continued to edit the journal until his illness in 1838 which led to his leaving India and subsequently his death. Many of the plates in the journal were illustrated by him.

Coins were Prinsep's first interest. He interpreted coins from Bactria and Kushan as well as Indian series coins, including "punch-marked" ones from the Gupta series. Prinsep suggested that there were three stages; the punch-marked, the die-struck, and the cast coins. Prinsep also reported upon the native punch-marked coinage, noting that they were better known in eastern India.

As a result of Prinsep's work as an editor of the Asiatic Society's journal, coins and copies of inscriptions were transmitted to him from all over India, to be deciphered, translated, and published.