Sir Thomas Mansell KCH (9 February 1777 – 1858) was a British Royal Navy rear admiral.

He entered the navy in January 1793, on board the Crescent frigate with Captain James Saumarez, whom he followed to the Orion, in which he was present in Lord Bridport's action off Lorient, at the battle of Cape St. Vincent, and the battle of the Nile; after which he was promoted by Nelson to be acting-lieutenant of the Aquilon, a promotion which was confirmed by the admiralty to 17 April 1799.

He was flag-lieutenant to Sir James Saumarez in the Diomede, Hibernia, and Victory, and on 17 September 1808 was promoted to the command of the Rose sloop, in which he took part in the capture of Anholt in the Baltic, 18 May 1809, and was at different times engaged with the Danish gunboats.

In 1812 he was presented by the emperor of Russia with a diamond ring, in acknowledgment of his having piloted a Russian squadron through the Belt; and by the king of Sweden with the order of the Sword, 'in testimony of the esteem in which he held his services.

The second, Arthur Lukis, for some years commanded the Firefly, surveying ship, in the Mediterranean, and died, a retired vice-admiral, in 1890.