The son of George Byng, Viscount Torrington, a prominent admiral, John entered the Royal Navy in 1718 and became a rear admiral in 1745. In 1755, on the eve of the Seven Years' War (1756–63), it was feared that the British base at Minorca would be attacked. Accordingly, three months before the outbreak of war, Byng was sent with an inadequate force to defend the island, but, by the time he arrived in May of that year, a French force under the Duke de Richelieu had already landed and was besieging Fort St. Philip. Byng fought a halfhearted engagement with a French fleet under the Marquis de La Galissonnière, and, at a council of war held afterward, he decided that his force was insufficient to either renew the attack or relieve the fort. He therefore returned to Gibraltar, leaving Minorca to the enemy. This failure aroused a storm of indignation in England, motivating Newcastle to promise that “he shall be tried immediately; he shall be hanged directly.” Byng was court-martialed on his own flagship in Portsmouth harbour; he was found guilty of neglect of duty and was executed by a firing squad of marines.

The episode provoked the French author Voltaire to remark in Candide that the English found it necessary from time to time to shoot an admiral “pour encourager les autres” (“in order to encourage the others”).