James Johnstone (c. 1759 – 1823) was a British naval officer and explorer.

He is noted for having served as sailing master of the armed tender HMS Chatham and later acting lieutenant during George Vancouver's 1791–1795 expedition to the Pacific Northwest.
The Johnstone Strait in British Columbia, Canada is named after him.

Johnstone sailed to the West Indies in 1798 and in September 1801, while acting as commander-lieutenant of the 18-gun ship-sloop Lark near Cuba, he captured the Spanish privateer-schooner Esperanza.

From 1811 to 1817 he served as Commissioner of the Navy in Bombay before being forced to return to Britain because of poor health.