John Knight was born in Dundee in February 1747, the son of Rear-Admiral Joseph Knight and his wife, Jean Hay. In 1758, aged 11, he followed his father into service with the Royal Navy aboard HMS "Tartar", participating in the Raid on Cherbourg that year during the Seven Years' War. Knight remained with his father for five more years, until moving at the end of the war in 1763 to HMS "Romney" on the North American station. Off North America, Knight participated in surveying operations and although he returned to Europe some years later, he went back to North America in 1775 at the start of the American Revolutionary War.