He was born in Birstall parish, 6 miles from Leeds, Yorkshire. He learned a variety of languages, both classical and modern, in his youth, including several Semitic languages; he also studied what was then called "natural history."
In 1751 he entered Daventry, a school under Nonconformist auspices, and there his religious views took shape. He became an adherent of Arianism. In September, 1755, he started as a parish minister in Surrey, though he was not officially ordained until May 18, 1762. Because he stammered and the parish was not suited to his heterodox ideas, nor did they want a bachelor for their minister, he was unpopular in his Surrey parish and he ultimately went to Nantwich, Cheshire. He established a private school in connection with the church in Nantwich where hepreached, and derived his income from that school.
Subsequently he went to Warrington, the biggest of the dissenting academies in England, as a tutor in belles-lettres. By this time his religious ideas had matured to a form of Unitarianism, Socinianism. At Warrington, he associated with other liberal-minded tutors and found an intelligent printer, William Eyres, willing to publish Priestley's work. It was here that he published his grammar book in 1761 (a remarkably liberal grammar for its day) and other books on history and educational theory. He taught anatomy and astronomy and led field trips for his students to collect fossils and botanical specimens. Both modern history and the sciences were subjects which had not been taught in any schools before Priestley.
On June 23, 1762, Priestley married Mary Wilkinson of Wrexham, and by September, 1767 the combination of his finances and her health caused him to relocate to Leeds. He there took charge of the Mill Hill congregation until December 1772. Then he was hired by William Petty, Lord Shelburne, as his personal librarian, and stayed in that post until 1780.
Whilst tutoring his benefactor's sons at Bowood House in 1774 he discovered oxygen, though a previous discovery by Karl Wilhelm Scheele, independently made, has actual priority. However he never recognized it as an element. He named the new gas (which he had generated by heating red mercuric oxide with a 'burning lens') 'de-phlogisticated air', in accordance with the Phlogiston theory which held at the time. In his experiments he managed to identify eight distinct gases, in contrast with the commonly held view of the time that there was just one 'air'.
In 1780 he moved to Birmingham and was appointed junior minister of the New Meeting Society. He became a member of the Lunar Society, but was driven out of the city in the Priestley Riots. He is remembered there by the Moonstones, and a more traditional statue.
He next moved to London where he received an invitation to become morning preacher at Gravel Pit Chapel, Hackney. His three sons emigrated to the United States in 1793, and in the following June Priestley followed them, seeking political and religious freedom. Although never being naturalized, he lived in Pennsylvania for the rest of his life.