James Rennell (December 3, 1742 - March 29, 1830) was a British geographer.

Rennell was born near Chudleigh in Devon. His father, an officer in the Artillery, was killed in action shortly after the birth of his son. He entered the navy as a midshipman in 1756, and was present at the attack on Cherbourg (1758), and the disastrous action of St Cast in the same year. At the end of the Seven Years War, seeing no chance of promotion, he entered the service of the East India Company, and was appointed surveyor of the Company's dominions in Bengal (1764), with the rank of captain in the Bengal Engineers. To this work he devoted the next thirteen years. In 1766 he received a severe wound in an encounter with some Sannyasis, or religious fanatics, from which he never thoroughly recovered; and in 1777 he retired as major on a pension of £600 a year.

The remaining fifty-three years of his life were spent in London, and were devoted to geographical research chiefly among the materials in the East India House. His most valuable works include the Bengal Atlas (1779), the first approximately correct map of India (1783), the Geographical System of Herodotus (1800), the Comparative Geography of Western Asia (1831), and important studies on the geography of northern Africa - in introductions to the Travels of Mungo Park and Hornemann - and the currents of the Atlantic and Indian Oceans. He also contributed papers to Archaeologia on the site of Babylon, the island of St Paul's shipwreck, and the landing-place of Caesar in Britain.

He was elected a fellow of the Royal Society in 1781; and he received the Copley Medal of the Royal Society in 1791, and the gold medal of the Royal Society of Literature in 1825. While in India he had married (1772) Jane Thackeray, a great-aunt of the novelist. He was buried in the nave of Westminster Abbey.

This article incorporates text from the public domain 1911 Encyclopædia Britannica.