Admiral of the Fleet Sir Thomas Byam Martin, GCB (25 July 1773 – 25 October 1854) was a Royal Navy officer and politician. As captain of fifth-rate HMS Fisgard he took part in a duel with the French ship Immortalité and captured her at the Battle of Tory Island during the French Revolutionary Wars. Then while in command of the third-rate HMS Implacable in the Baltic Sea and attached to the Swedish Navy he took part in the capture the Russian ship Sewolod (Vsevolod) during the Napoleonic Wars. During the French invasion of Russia, Martin commanded British naval squadron supporting Russian defenders in the siege of Riga.

During his many years of service as Comptroller of the Navy, Martin was credited with reducing the fleet from the enormous size deployed against the French to a much more streamlined service geared toward protecting merchant trade and the British Empire. He also focused heavily on employing highly trained dockyard staff capable of responding rapidly to any international emergency. Martin also sat in Parliament for 14 years and was an outspoken critic of government attempts to reduce the Navy budget which ultimately saw him dismissed in 1831 by his old friend King William IV.

Martin died in October 1854, at the early stages of the Crimean War, planning the Baltic Campaign and investigating the possibilities of using poison gas weapons.

Born the third son of Sir Henry Martin, 1st Baronet (later MP for Southampton) and his wife Eliza Anne Gillman (née Parker), Martin was educated at Freshford School, Southampton Grammar School and later the Royal Grammar School, Guildford. During his education, he was also enrolled on the books of several Navy ships, a custom of the period to ensure that when he was old enough to go to sea he already would have the requisite "experience" to be considered for promotion early.

Martin joined the Royal Naval College, Portsmouth in August 1785 and went to sea for the first time as a captain's servant aboard the sixth-rate HMS Pegasus, captained by Prince William Henry, on the North American Station in April 1786. Promoted to midshipman, he transferred to fifth-rate HMS Andromeda in March 1788 and subsequently to the third-rate HMS Colossus, the fifth-rate HMS Southampton, the second-rate HMS Barfleur and then the first-rate HMS Royal George.

Promoted to lieutenant on 22 October 1790, Martin served in the third-rate HMS Canada in the Channel Squadron and subsequently in the fifth-rate HMS Inconstant and the fifth-rate HMS Juno. He was promoted to commander on 22 May 1793 and given command of the fire ship HMS Tisiphone in the Mediterranean Fleet.

Martin was promoted to captain on 5 November 1793 and given command of the fifth-rate HMS Modeste, a frigate recently captured from the French, and saw action in operations off Toulon at an early stage of the French Revolutionary Wars. He went on to command the fifth-rate HMS Artois and saw action at the siege of Bastia in April 1794. Martin was then transferred to the Channel Fleet and stationed off Ireland in HMS Santa Margarita, in which he captured the French frigate Tamise at the Atlantic raid of June 1796: in the engagement, Tamise was badly damaged and suffered heavy casualties while HMS Santa Margarita's losses were only two killed and three wounded.

In December 1796, Martin was sent to the West Indies as captain of the fifth-rate HMS Tamar in which he captured nine privateers. He then moved to the command of the third-rate HMS Dictator before taking over the newly captured fifth-rate HMS Fisgard. On 20 October 1798 HMS Fisgard took part in a duel with the French ship Immortalité and captured her at the Battle of Tory Island. Martin continued to be employed off the French coast, capturing merchant vessels, privateers and warships.