HMS Zealous was a 74-gun third-rate ship of the line of the Royal Navy, built by Barnard of Deptford and launched on 25 June 1785.

She served in a number of battles of the French Revolutionary Wars and the Napoleonic Wars, notably the Battle of the Nile, where she engaged the French ship Guerrier, helping to force her surrender. She was later cruising off Cadiz in 1801. She missed out on the Battle of Trafalgar, having been dispatched to Gibraltar for resupply.

After Trafalgar, Zealous continued in the blockade of Cadiz. On 25 November 1805, Thunderer detained the Ragusan ship Nemesis, which was sailing from Isle de France to Leghorn, Italy, with a cargo of spice, indigo dye, and other goods. Zealous shared the prize money with ten other British warships.

Zealous was later assigned to convoy duty in the Mediterranean.