Sir John McNeill GCB PC FRSE FRAS (1795 – 17 May 1883) was a Scottish surgeon and diplomat.
McNeill was born on 12 August 1795 at Oronsay House on the island of Oronsay in the Inner Hebrides. He was the third of the six sons of John McNeill, laird of Colonsay and Oronsay (1767–1846) and his wife, Hester McNeill (died 1843). He was the younger brother of the law lord Duncan McNeill, 1st Baron Colonsay and Oronsay.
He studied medicine at the University of Edinburgh, where he graduated as a Doctor of Medicine in 1814, at the age of nineteen.
On 6 September 1816 he was appointed assistant surgeon on the Honourable East India Company's Bombay establishment. He was moved to Persia in 1819. He received his licence as a surgeon on 1 May 1824 and retired from the medical service on 4 June 1836, thereafter concentrating on the diplomatic aspects of the East India Company.
He was attached to the field force under Colonel East in Kutch and Okamundel in 1818–19 and was afterwards deputy medical storekeeper at the presidency.
From 1824 to 1835, he was attached to the East India Company's legation in Persia, at first in medical charge, and latterly as political assistant to the Minister, John Macdonald Kinneir, in which post he displayed great ability. For instance, in 1829 he was probably one of the instigators of the murder of Alexander Griboyedov by Persian mob in Teheran.