HMS Leviathan was a 74-gun third-rate ship of the line of the British Royal Navy, launched on 9 October 1790.
At the Battle of Trafalgar under Henry William Bayntun, she was near the front of the windward column led by Admiral Lord Nelson aboard his flagship, , and captured the Spanish ship . A flag said to have been flown by the Leviathan at Trafalgar is to be sold at auction by Arthur Cory in March 2016 - Bayntun is thought to have given it to his friend the Duke of Clarence (later William IV), who then gave it to Arthur Cory's direct ancestor Nicholas Cory, a senior officer on William's royal yacht , in thanks for helping the yacht win a race and a bet.
Leviathan, , , , and shared in the proceeds of the capture on 10 September 1797 of the Tordenskiold.
In 1809, she took part in the Battle of Maguelone.
On 27 June 1812, Leviathan, , and attacked an 18-strong French convoy at Laigueglia and Alassio in Liguria, northern Italy.
In 1816, after the end of the Napoleonic Wars, she was converted into a prison ship and in 1848 was sold and broken up.