Sir James Emerson Tennent, 1st Baronet, FRS (born James Emerson; 7 April 1804 – 6 March 1869) was a Conservative Member of the United Kingdom Parliament for the Irish seats of Belfast and of Lisburn, and a resident Colonial Secretary in Ceylon. Opposed to the restoration of a parliament in Dublin, his defence of Ireland's union with Great Britain emphasised what he conceived as the liberal virtues of British imperial administration. In Ceylon, his policies in support the growing plantation and wage economy met with peasant resistance in the Matale Rebellion of 1848. In recognition of his encyclopedic surveys of the colony, in 1862 he was elected a Fellow of the Royal Society.

He was born in North Street, Belfast, on 7 April 1804, third and only surviving son of William Emerson (d. 1821), of Ardmore, County Armagh, a wealthy tobacco merchant, and Sarah, youngest daughter of William Arbuthnot of Ardmore, County Armagh. He was educated at the Belfast Academy and at Trinity College.

With his college friend, Robert James Tennent, he took up the cause of Greek independence. At the beginning of 1824 he travelled to Greece, and when he arrived in Messolonghi, joined the artillery corps formed by Lord Byron. He was to remain at the side of the poet until his death in April. After a respite of some months in England, he returned to Greece in March 1825. Appointed a captain of artillery, some sources place him in the battle to break the Siege of the Acropolis in Athens.

In 1826 he published in London his first book entitled Picture of Greece, which contributed to the development of the philhellenic sentiment in Great Britain. It was followed by Letters from the Aegean (1829), and a History of Modern Greece (1830). He also authored a series of unsigned articles in the British press, supporting the Greek struggle.

In 1831, with the support of Jeremy Bentham, he was called to the English bar at Lincoln's Inn. That same year, he married his friend's cousin, Letitia, co-heiress to the mercantile fortune of her father, the Belfast merchant-patrician (and former United Irishman) William Tennent. After his father-in-law's death in 1832, by royal licence Emerson added Tennent to his family name.

Following the Reform Act 1832, both he and Robert Tennent decided to contest the first open election for the two-seat Belfast constituency, previously in the "pocket" of the town's proprietor, Lord Donegall. Emerson choose to stand as an Independent Whig in the Donegall interest, while (consistent with both is father's and his uncle's democratic politics) stood as a Whig on a platform of further reform. Emerson Tennent and a Tory candidate prevailed in a victory that Protestant loyalists celebrated with an attack on the central Catholic district (Hercules Street) and with an attempt to ransack Robert Tennent's house.

Once in Parliament, Emerson Tennent took the Tory whip. He supported Sir Robert Peel in his first ministry (1834–35), but broke with his "liberal Conservatives" over the repeal of the Corn Laws in his second (1841–46). He joined the moderate Conservative followers of Edward Smith-Stanley, the Earl of Derby.

Replying to Daniel O'Connell in the 1834 Commons debate on Repeal of the Union, Emerson Tennent sought to eschew the Protestant sectionalism and fear of Catholicism, generally assumed to be the central elements of unionist thought. Instead, he raised issues close to O'Connell heart as a campaigning abolitionist. Reflecting on the recent vote to suppress slavery in the British Empire, he remarked: