At the age of 14 he ran away from home to join a merchant ship. In 1804 he was in the East India Company's ship "Marquis Cornwallis", which the government chartered for an expedition against the Seychelles. In the following March, as the vessel was bought by the Royal Navy to be a 50-gun ship under the command of Captain Charles James Johnston, with whom Smyth remained, seeing much active service in Indian, Chinese, Australian and Pacific waters. In February 1808 he followed Johnston to , which, on returning to England, was part of the force in the expedition to the Scheldt, and was paid off in October 1809. He afterwards served in the 74-gun on the coast of France and Spain, and was lent from her to command the Spanish gunboat "Mors aut Gloria" at the defence of Cadiz from September 1810 to April 1811. In July 1811 he joined off Toulon, and through 1812 served on the coast of Spain.