Leslie, Thomas Edward Cliffe (1825–82), political economist, was born 21 June 1825 in Co. Wexford, second son of the Rev. Edward Leslie and Margaret Leslie (née Higginson), who had also at least five daughters. His father was a member of the Leslie family of Glaslough, and a half-brother of John Leslie, bishop of Dromore, who presented him to the living of Anahilt, Co. Down; his wife was daughter of a Lisburn clergyman, Thomas Higginson. Thomas's father taught him until he was ten, when he was sent to King William's College on the Isle of Man.
In October 1842 he entered TCD and won a scholarship in 1845; he graduated (1847) as senior moderator and with the gold medal in ethics and logic. His classmates included several men who were after wards prominent in economics or political economy – John E. Cairnes (qv), W. E. Hearn (qv), and Richard Walsh (qv). Leslie was enrolled in King's Inns in 1846, and in Lincoln's Inn in London in 1848; he was called to the Irish bar in 1850 and took his LLB in TCD in 1851. In 1857 he was called to the English bar, but never practised; in 1853 he had been appointed professor of jurisprudence and political economy at QCB.
His health was poor, and he lived mostly in London, where he published a great deal and earned a reputation as a political economist; he was aware of the pioneering work of Auguste Comte and introduced European developments in sociology to students in Britain. He was largely responsible for the development in the UK of the historical and comparative approach to economic questions. His opposition to the existing deductive model of economics was most notably expressed in an article in Hermathena in 1876. He published in 1856 a volume on the effect on commerce of the militarism of his day, and his Land systems and industrial economy of Ireland, England and continental countries (1870) was regarded as a valuable summary of the various land tenure arrangements in Europe; John Stewart Mill reviewed it very favourably in the Fortnightly Review. Leslie contributed numerous articles to journals and reviews; many were republished in Essays on political and moral philosophy (1879).
What would possibly have been Leslie's chef d'oeuvre on the economic history of England, in which legal customs and history were treated as major influences, was lost in manuscript during the author's travels in Europe in 1872, and he was unable to recreate it. Leslie was elected without a ballot to the Athenæum, and was awarded an honorary LLD by TCD in 1878; he was an honorary member of the Société d'Economie Politique de Paris. He died after years of ill health at his house on Botanic Avenue, Belfast, on 27 January 1882.