He was a prominent puritan opponent of the church policy of the Archbishop of Canterbury, William Laud.
Born at Swainswick, near Bath, he was educated at Bath Grammar School and Oxford. He was admitted a student of Lincoln's Inn in 1621, and was called to the bar in 1628.
Like many Puritans abhorring decadent celebrations he was strongly opposed to religious feast days, including Christmas, and revelry such as stage plays.
In 1632 William Noy as Attorney-General instituted proceedings against Prynne in the Star-chamber. After a year's imprisonment in the Tower of London, he was sentenced to be imprisoned for life, to be fined £5,000, to be expelled from Lincoln's Inn, to be deprived of his degree by the university of Oxford, and to lose both his ears in the pillory. Prynne was pilloried on 7 May and 10 May.
His imprisonment was then much closer: no pens and ink, and allowed no books except the Bible, the prayer-book, and some orthodox theology. To isolate him from his friends he was removed first to Carnarvon Castle (July 1637), and then to Mont Orgueil Castle in Jersey. The governor, Sir Philip Carteret, treated Prynne well, which he repaid by defending Carteret's character in 1645 when he was accused as a malignant and a tyrant. He occupied his imprisonment by writing verse.
He was released by the Long Parliament in 1640. The House of Commons declared the two sentences against him illegal, restored him to his degree and to his membership of Lincoln's Inn, and voted him pecuniary reparation. He supported the Parliamentary cause in the English Civil War, particularly in the press, and in many pamphlets.
He was able to have the satisfaction of overseeing the trial of William Laud, which was to end in Laud's execution. He collected and arranged evidence to prove the charges against him, bore testimony himself in support of many of them, hunted up witnesses against the archbishop, and assisted the counsel for the prosecution in every way.
During 1647 the breach between the army and the Parliament turned Prynne's attention from theology to politics. He wrote a number of pamphlets against the army, and championed the cause of the eleven presbyterian leaders whom the army impeached.
In November 1648 Prynne was elected Member of Parliament for Newport,Cornwall for the Long Parliament. As soon as he took his seat, he showed his opposition to the army. He urged the Commons to declare them rebels, and two days later he was arrested by Colonel Thomas Pride.
Released from custody some time in January 1649, Prynne retired to Swanswick, and began a paper war against the new government. He became a thorn in Cromwell's side. The government retaliated by imprisoning him for nearly three years without a trial. He was finally offered his liberty on 18 February 1653.
Prynne supported the Restoration, and was rewarded with public office. In April 1660 he was elected MP for Bath in the Convention Parliament. As a politician Prynne was during his latter years of minor importance. He became the Keeper of Records in the Tower of London and died unmarried on 24 October 1669.