Elphinstone entered the British Army in 1804 as a lieutenant; he saw service throughout the Napoleonic Wars, rising to the rank of lieutenant-colonel by 1813, when he became commander of the 33rd Regiment of Foot, which he led at the Battle of Waterloo in 1815.

[4] Confirmed in his appointment in December 1840, Elphinstone took command of the British garrison in Kabul, Afghanistan, numbering around 4,500 troops, of whom 690 were European and the rest Indian.

Elphinstone completely failed to lead his soldiers, but fatally exerted enough authority to prevent any of his officers from exercising proper command in his place.

Present at his death was the Military Secretary George Lawrence, who while under no illusions as to Elphinstone's unsuitability for his command, commented "His kind, mild disposition and courteous detachment had made him esteemed by us all".

En route, they were attacked by a band of tribesmen who stripped and abused the corpse until it was rescued by horsemen sent by the Afghan leader Akbar Khan.