John Sibthorp (1758–1796) was an English botanist

Sibthorp was born on October 28 1758 in Oxford, the youngest son of Dr Humphrey Sibthorp (1713–1797), who from 1747 to 1784 was Sherardian professor of botany at the University of Oxford.

He graduated from Oxford in 1777, and then studied medicine at the Universities of Edinburgh and Montpellier. In 1784 he succeeded his father to the Sherardian chair. Leaving his professional duties to a deputy, he left England for Göttingen and Vienna, in preparation for a botanical tour of Greece (1786).

Returning to England at the end of the following year, he took part in the foundation of the Linnaean Society in 1788, and set to work on a flora of Oxfordshire, which was published in 1794 as Flora Oxoniensis. He made a second journey to Greece, but developed consumption on the way home' and died in Bath on 8 February 1796.

His will bequeathed his books on natural history and agriculture to the University of Oxford, and also founded Oxford's Sibthorpian professorship of rural economy (held by Chris J Leaver as of 2005), attaching it to the chair of botany. He directed that the endowment should first be applied to the publication of his Flora Graeca and Florae Graecae Prodromus, for which, however, he had done little beyond collecting some three thousand species and providing the plates. The task of preparing the works was undertaken by Sir J.E. Smith , who issued the two volumes of the Prodromus in 1806 and 1813, and six volumes of the Flora Graeca between 1806 and 1828. The seventh appeared in 1830, after Smith's death, and the remaining three were produced by John Lindley between 1833 and 1840.

The standard botanical author abbreviation Sibth. is applied to species he described.