CLARKSON, THOMAS (176o-1846), English anti-slavery agitator, was born on March 28, 1760, in Wisbech, Cambs., the son of a schoolmaster. He was educated at St. Paul's school and St. John's college, Cambridge. Clarkson was first drawn to the subject of slavery by reading Benezet's Historical Survey of New Guinea (for a prize essay in 1785) on the question set by the vice chancellor of the university : "Is it right to make men slaves against their will?" The English translation of the Latin of this prize essay, published in 1786, brought him into touch with Wil Liam Dillwyn, Joseph Wood and Granville Sharp, and soon a com mittee of 12 was formed to do all that was possible to effect the abolition of the slave trade. Meanwhile Clarkson gained the sympathy of Wilberf orce, Whitbread, Pitt, Grenville, Fox and Burke, and spent his days in travelling from port to port, gaining a mass of evidence which was partly embodied in his Summary View of the Slave Trade, and the Probable Consequences of its Abolition. In May 1788 Pitt introduced a parliamentary discus sion on the subject, and Sir W. Dolben brought forward a bill, which was passed in the House of Commons on June 18, provid ing that the number of slaves carried in a vessel should be propor tional to its tonnage. In the same year, Clarkson published an Essay on the Irnpolicy of the Slave Trade, but could only get nine men, personally acquainted with the facts of the trade, to promise to appear before the Privy Council. Wilberforce and the committee, however, had obtained other witnesses, and in May 1789 the former led a debate on the subject in the House of Commons, in which he was seconded by Burke and supported by Pitt and Fox.
At the outbreak of the French Revolution, Clarkson hoped that the French would sweep away slavery with other abuses ; but the hope was vain, and of ter six months in Paris during which he enlisted the sympathies of Necker, Mirabeau and the Marquis de la Fayette, he returned to England and to his laborious search for further witnesses of the slave traffic. After his health gave way in 1794, Clarkson laid aside active work for writing, pub lishing in 1806 Portraiture of Quakerism, and, two years later, the History of the Rise, Progress and Accomplishment of the Abolition of the Slave Trade by the Brit. Parliament. The bill for the abolition had become law in 5807, and finally, in 1815, British diplomacy secured the condemnation of the trade by the other Great Powers. When the question of practical measures for its abolition was unsuccessfully discussed at the Congress of Aix-la-Chapelle in 1818, Clarkson personally presented an address to the emperor, Alexander I., who communicated it to the sovereigns of Austria and Prussia. In 1823 the Anti-Slavery Society was formed with Clarkson as its vice-president.
From this date until his death at Ipswich on Sept. 26, 1846, his chief works were Thoughts on the Necessity for Improving the Condition of the Slaves in the British Colonies (1823), and American Slavery (1845). His Memoirs of William Penn had appeared in 1813. See T. Elmes, Thomas Clarkson (1854).