George Johnstone was a Royal Navy officer who saw service during the War of the Austrian Succession, the Seven Years' War and the American War of Independence, rising to the rank of post-captain and serving for a time as commodore of a British naval squadron. In a multifaceted career he was also a member of parliament, a director of the East India Company, a member of the Carlisle Peace Commission and the first Governor of West Florida from 1763 until 1767.

The Carlisle Peace Commission was a group of British peace commissioners who were sent to North America in 1778 to negotiate terms with the rebellious Continental Congress during the American Revolutionary War. The commission carried an offer of self-rule, including parliamentary representation within the British Empire. The Second Continental Congress, aware that British troops were about to be withdrawn from Philadelphia, insisted on demanding full independence, which the commission was not authorised to grant.