A career military officer, Henry Gladwin served mostly in North America. He had achieved the rank of major by 1759. In 1762, Lord Jeffrey Amherst gave him command of the Fort Detroit garrison.

On the evening of May 6, 1762, Gladwin received word from a secret informer that Pontiac and his followers planned to take over Detroit. When Pontiac showed up the following day with 150 warriors carrying concealed weapons, Gladwin was able to thwart their plan.

Unable to take Detroit by stealth, Pontiac had his warriors besiege it. The siege lasted five months. Gladwin steadfastly rejected all of Pontiac's offers to let him and his soldiers go unharmed if they gave up Fort Detroit.

Gladwin went back to England shortly after Pontiac abandoned the siege of Detroit. For his reward, he was promoted to major general. He never returned to North America. Retiring from the army shortly after his promotion, Gladwin spent the rest of his life on his English country estate. He died in 1791.