Smith entered the Navy in 1777 and served in North America and the West Indies, where in 1780 he was promoted to lieutenant. After the American War of Independence, he travelled in France, North Africa and the Baltic as a government agent and at the outbreak of the Revolutionary War he was in Smyrna. He joined Hood at Toulon and took part in its evacuation and burning. In 1794 he was employed in the North Sea and in 1796 off Le Havre, where he was captured during a cutting-out expedition. For two years he was a prisoner but escaped in 1798, when he was given command of Tigre as senior officer in the Levant. In 1799 his success at the defence of Acre halted the advance of the French army. He was elected Member of Parliament for Rochester in 1802. On the resumption of the war Smith commanded a squadron off Holland. In 1805 he was promoted to rear-admiral and went to the Mediterranean where he was active off the coast of South Italy. He took part in the expedition to the Dardanelles in 1807 and in the following year went briefly to the South American Station. In 1810 he was promoted to vice-admiral and went in 1812 to be second-in-command of the Mediterranean Station, returning in bad health in 1814. He saw no further active service and retired to Paris after 1815, and pursued a campaign against the slavery of Europeans and Africans in north African countries as the president of the Knights Liberators of the Slaves in Africa and the Anti-Pirate Society. He was made an admiral in 1821. Among the biographies are Sir John Barrow, 'Life and correspondence of Admiral Sir William Sidney Smith, G. C. B.' (London, 1848), Edward Russell, 2nd Baron of Liverpool, 'Knight of the sword; the life and letters of Admiral Sir William Sidney Smith, C. C. B.' (London, 1964) and Tom Pocock 'A Thirst for Glory: The Life of Admiral Sir Sidney Smith' (London, 1996).