He prepared for the Presbyterian ministry and served several churches in England as pastor but gradually rejected orthodox Calvinism and adopted Unitarian views. His Essay on Government (1768) suggested the idea of “the greatest happiness of the greatest number” to Jeremy Bentham. In 1769 he founded the Theological Repository for critical discussion. In his History of Electricity (1767), he explained the rings (known as Priestley's rings) formed by a discharge upon a metallic surface. His improvements in the manipulation of gases enabled him to investigate the properties of gases and to discover new ones, including sulfur dioxide, ammonia, and what Priestly called “dephlogisticated air,” the gas that Lavoisier named oxygen and made the basis of experiments that were the foundation of modern chemistry. Priestley himself failed to realize the importance of his discovery of oxygen. His Examination of Scottish Philosophy appeared in 1774; his History of the Corruptions of Christianity, published in 1782, was officially burned in 1785; and his History of Early Opinions concerning Jesus Christ appeared in 1786. In 1790 he wrote two volumes of a General History of the Christian Church to the Fall of the Western Empire, and four volumes of the later history of the church appeared between 1802 and 1803. In the meantime he pursued his scientific and philosophical studies; opposed orthodox doctrines, the government's colonial policy, and slave trade; advocated the repeal of the Test Act and Corporation Act; and carried on a seven-year controversy (1783–90) with the Rev. Samuel Horsley. His sympathy with the aims of the French Revolution aroused popular prejudice against him, which led in 1791 to the wrecking of his house and the destroying of his library and scientific apparatus. Priestley emigrated to the United States in 1794 and lived at Northumberland, Pa., for the remainder of his life. He continued his chemical experimentation and engaged in a controversy on the phlogiston theory with leading American chemists. His Theological and Miscellaneous Works, in 25 volumes, edited by J. T. Rutt, were published between 1817 and 1832.
See his letters, ed. by R. E. Schofield (1966); his memoirs (2 vol., 1806, repr. 1970); Lester Kieft and Bennett R. Willeford, Jr., Joseph Priestley: Scientist, Theologian, and Metaphysician (1979); James J. Huecher, Joseph Priestley and the Idea of Progress (1987); bibliography by R. E. Crook (1966).