Percy Bysshe Shelley (4 August 1792 – 8 July 1822) was one of the major English Romantic poets and is critically regarded among the finest lyric poets in the English language. Shelley was famous for his association with John Keats and Lord Byron. The novelist Mary Shelley was his second wife.

He is most famous for such classic anthology verse works as Ozymandias, Ode to the West Wind, To a Skylark, and The Masque of Anarchy, which are among the most popular and critically acclaimed poems in the English language. His major works, however, are long visionary poems which included Alastor, Adonaïs, The Revolt of Islam, and the unfinished work The Triumph of Life. The Cenci (1819) and Prometheus Unbound (1820) were dramatic plays in five and four acts respectively. He wrote the Gothic novels Zastrozzi (1810) and St. Irvyne (1811) and the short works The Assassins (1814) and The Coliseum (1817). Shelley's unconventional life and uncompromising idealism, combined with his strong disapproving voice, made him an authoritative and much-denigrated figure during his life and afterward. Shelley never lived to see the extent of his success and influence. Some of his works were published, but they were often suppressed upon publication. Up until his death, with approximately 50 readers as his audience, it is said he made no more than 40 pounds from his writings. He became an idol of the next three or even four generations of poets, including the important Victorian and Pre-Raphaelite poets. He was admired by Karl Marx, George Bernard Shaw, Bertrand Russell, Isadora Duncan and Jiddu Krishnamurti ("Shelley is as sacred as the Bible.") Henry David Thoreau's civil disobedience and Mohandas Karamchand Gandhi's passive resistance were influenced and inspired by Shelley's nonviolence in protest and political action.

A son of Sir Timothy Shelley, a Whig Member of Parliament, and his wife, a Sussex landowner, Shelley was born at Field Place in Broadbridge Heath, near Horsham, England. He was the eldest of 7 children with 5 sisters and one brother. He received his early education at home, tutored by Reverend Evan Edwards of Warnham. His cousin and lifelong friend Thomas Medwin, who lived nearby recounted his early childhood in his "The Life of Percy Bysshe Shelley". It was a happy and contented childhood spent largely on country pursuits such as fishing and hunting. In 1802, he entered the Syon House Academy of Brentford. In 1804, Shelley entered Eton College, where he fared poorly, subjected to an almost daily mob torment his classmates called "Shelley-baits". Surrounded, the young Shelley would have his books torn from his hands and his clothes pulled at and torn until he cried out madly in his high-pitched "cracked soprano" of a voice.

On 10 April 1810, he matriculated at University College, Oxford. Legend has it that Shelley attended only one lecture while at Oxford, but frequently read sixteen hours a day. His first publication was a Gothic novel, Zastrozzi (1810), in which he vented his atheistic worldview through the villain Zastrozzi. In the same year, Shelley, together with his sister Elizabeth, published Original Poetry by Victor and Cazire. While at Oxford, he issued a collection of verses (perhaps ostensibly burlesque but quite subversive), Posthumous Fragments of Margaret Nicholson, with Thomas Jefferson Hogg. In 1811, Shelley published his second Gothic novel St. Irvyne; or, The Rosicrucian and a pamphlet called The Necessity of Atheism. This gained the attention of the university administration and he was called to appear before the College's fellows, including the Dean, George Rowley. His refusal to repudiate the authorship of the pamphlet resulted in his being sent down from Oxford on 25 March 1811, along with Hogg. The rediscovery in mid-2006 of Shelley's long-lost 'Poetical Essay on the Existing State of Things', a long, strident anti-monarchical and anti-war poem printed in 1811 in London by Crosby and Company as "by a gentleman of the University of Oxford", gives a new dimension to the expulsion, reinforcing Hogg's implication of political motives ('an affair of party'). Shelley was given the choice to be reinstated after his father intervened, on the condition that he would have had to recant his avowed views. His refusal to do so led to a falling-out with his father.

Four months after being expelled, the 19-year-old Shelley eloped to Scotland with the 16-year-old schoolgirl Harriet Westbrook to get married. After their marriage on 28 August 1811, Shelley invited his college friend Hogg to share their household. When Harriet objected, however, Shelley brought her to Keswick in England's Lake District, intending to write. Distracted by political events, he visited Ireland shortly afterward in order to engage in radical pamphleteering. Here he wrote his Address to the Irish People and was seen at several nationalist rallies. His activities earned him the unfavourable attention of the British government. Unhappy in his nearly three-year-old marriage, Shelley often left his wife and child (Ianthe Shelley, 1813–76) alone, first to study Italian with a certain Cornelia Turner, and eventually to visit William Godwin's home and bookshop in London. There he met and fell in love with Godwin's eldest daughter, named after her mother Mary Wollstonecraft, the author of A Vindication of the Rights of Woman, among others.

On 28 July 1814, Shelley abandoned his pregnant wife and child when he ran away with Mary, then also 16, inviting her stepsister Claire Clairmont along for company. The three sailed to Europe, crossed France, and settled in Switzerland, an account of which was subsequently published by the Shelleys. After six weeks, homesick and destitute, the three young people returned to England. In late 1815, while living close to London with Mary and avoiding creditors, he wrote Alastor, or The Spirit of Solitude. It attracted little attention at the time, but has now come to be recognized as his first major achievement. At this point in his writing career, Shelley was deeply influenced by the poetry of Wordsworth. In mid-1816, Shelley and Mary made a second trip to Switzerland. They were prompted to do so by Mary's stepsister Claire Clairmont, who had commenced a liaison with Lord Byron the previous April just before his self-exile on the continent. Byron had lost interest in her and so she used the opportunity of meeting the Shelleys to act as bait to lure him to Geneva. The Shelleys and Byron rented neighbouring houses on the shores of Lake Geneva. Regular conversation with Byron had an invigorating effect on Shelley's output of poetry. While on a boating tour the two took together, Shelley was inspired to write his Hymn to Intellectual Beauty, often considered his first significant production since Alastor. A tour of Chamonix in the French Alps inspired Mont Blanc, a poem in which Shelley claims to have pondered questions of historical inevitability and the relationship between the human mind and external nature.

After the Shelleys returned to England, Fanny Imlay, Mary's half-sister and Claire's stepsister, travelled from Godwin's household in London to kill herself in Wales in early October. In December 1816, Shelley's estranged wife Harriet drowned herself in the Serpentine in Hyde Park, London. On 30 December 1816, a few weeks after Harriet's body was recovered, Shelley and Mary Godwin were married. The marriage was intended, in part, to help secure Shelley's custody of his children by Harriet, but the plan failed: the courts gave custody of the children to foster parents due to the fact that he was an atheist.

The Shelleys took up residence in the village of Marlow, Buckinghamshire, where a friend of Percy's, Thomas Love Peacock, lived. Shelley took part in the literary circle that surrounded Leigh Hunt, and during this period he met John Keats. Shelley's major production during this time was Laon and Cythna; or, The Revolution of the Golden City, a long narrative poem in which he attacked religion and featured a pair of incestuous lovers. It was hastily withdrawn after only a few copies were published. It was later edited and reissued as The Revolt of Islam in 1818. Shelley wrote two revolutionary political tracts under the nom de plume, "The Hermit of Marlow."

Early in 1818, the Shelleys and Claire left England in order to take Claire's daughter, Allegra, to her father Byron, who had taken up residence in Venice. Contact with the older and more established poet encouraged Shelley to write once again. During the latter part of the year, he wrote Julian and Maddalo, a lightly disguised rendering of his boat trips and conversations with Byron in Venice, finishing with a visit to a madhouse. This poem marked the appearance of Shelley's "urbane style". He then began the long verse drama Prometheus Unbound, a re-writing of the lost play by the ancient Greek poet Aeschylus, which features talking mountains and a petulant spirit who overthrows Jupiter. Tragedy struck in 1818 and 1819, when his son Will died of fever in Rome, and his infant daughter Clara Everina died during yet another household move. A daughter, Elena Adelaide Shelley, was born on 27 December 1818 in Naples, Italy and registered there as the daughter of Shelley and a woman named Marina Padurin. However, the identity of the mother is an unsolved mystery. Some scholars speculate that her true mother was actually Claire Clairmont or Elise Foggi, a nursemaid for the Shelley family. Other scholars postulate that she was a foundling Shelley adopted in hopes of distracting Mary after the deaths of William and Clara. Shelley referred to Elena in letters as his "Neapolitan ward". However, Elena was placed with foster parents a few days after her birth and the Shelley family moved on to yet another Italian city, leaving her behind. Elena died 17 months later, on 10 June 1820.

The Shelleys moved around various Italian cities during these years. In later 1818 they were living in a pensione on the Via Valfonde (which now runs alongside Florence train station). The pensione was destroyed in World War II but there is a plaque on the building which replaced it. Here, they received two visitors, a Miss Sophia Stacey and her much older travelling companion, Miss Corbet Parry-Jones (to be described by Mary as 'an ignorant little Welshwoman'). Sophia had for three years in her youth been ward of the poet's aunt and uncle. Hitting it off the pair moved into the same pensione and stayed for about two months. During this period Mary gave birth to her son and Sophia is credited with suggesting that he be named after the city of his birth, so he became Percy Florence Shelley, later Sir Percy. Shelley also wrote his 'Ode to Sophia Stacey' now in all complete collections of his work. Shelley completed Prometheus Unbound in Rome, and he spent mid-1819 writing a tragedy, The Cenci, in Livorno. In this year, prompted among other causes by the Peterloo massacre, he wrote his best-known political poems: The Masque of Anarchy and Men of England. These were most likely his most-remembered works during the 19th century. Around this time period, he wrote the essay The Philosophical View of Reform, which was his most thorough exposition of his political views to that date.

In 1820, hearing of John Keats' illness from a friend, Shelley wrote him a letter inviting him to join him at his residence at Pisa. Keats replied with hopes of seeing him, but instead, arrangements were made for Keats to travel to Rome with the artist Joseph Severn. Inspired by the death of Keats, in 1821 Shelley wrote the elegy Adonais. In 1821, Shelley met Edward Ellerker Williams, a British naval officer and his wife Jane. Shelley developed a very strong affection towards Jane and addressed a number of poems to her. Shelley's affection for Jane was pure and platonic, almost bordering on devotion. In the poems addressed to Jane, like With a Guitar, To Jane and One Word is Too Often Profaned, he elevates her to an exalted position worthy of worship. In 1822, Shelley arranged for Leigh Hunt, the British poet and editor who had been one of his chief supporters in England, to come to Italy with his family. He meant for the three of them — himself, Byron and Hunt — to create a journal, which would be called The Liberal. With Hunt as editor, their controversial writings would be disseminated, and the journal would act as a counter-blast to conservative periodicals such as Blackwood's Magazine and The Quarterly Review. Leigh Hunt's son, the editor Thornton Leigh Hunt, when later asked whether he preferred Shelley or Byron as a man, replied:-

"On one occasion I had to fetch or take to Byron some copy for the paper which my father, himself and Shelley, jointly conducted. I found him seated on a lounge feasting himself from a drum of figs. He asked me if I would like a fig. Now, in that, Leno, consists the difference, Shelley would have handed me the drum and allowed me to help myself."

"Don Juan", a compliment to Byron, was chosen by Edward John Trelawny, a member of the Shelley-Byron Pisan circle. However, according to Mary Shelley's testimony, Shelley changed it to "Ariel". This annoyed Byron, who forced the painting of the words "Don Juan" on the mainsail. This offended the Shelleys, who felt that the boat was made to look much like a coal barge. The vessel, an open boat, was custom-built in Genoa for Shelley. It did not capsize but sank; Mary Shelley declared in her "Note on Poems of 1822" (1839) that the design had a defect and that the boat was never seaworthy. In fact the boat was seaworthy, the sinking was due to the storm and poor seamanship of the three on board.

There were those who believed his death was not accidental. Some said that Shelley was depressed in those days and that he wanted to die; others that he did not know how to navigate; others believed that some pirates mistook the boat for Byron's and attacked him, and others have even more fantastical stories. There is a mass of evidence, though scattered and contradictory, that Shelley may have been murdered for political reasons. Previously, at his cottage in Tann-yr-allt in Wales, he had been surprised and apparently attacked by a man who may have been an intelligence agent. In the days before he died, he was almost shot on two separate occasions. A British consul defended the shooter from the first of these two incidents, keeping him from all legal consequence.

Two other Englishmen were with Shelley on the boat. One was a retired Navy officer, Edward Ellerker Williams; the other was a boatboy, Charles Vivien. The boat was found ten miles (16 km) offshore, and it was suggested that one side of the boat had been rammed and staved in by a much stronger vessel. However, the liferaft was unused and still attached to the boat. The bodies were found completely clothed, including boots. In his 'Recollections of the Last Days of Shelley and Byron', Trelawny noted that the shirt that Williams's body was clad in was 'partly drawn over the head, as if the wearer had been in the act of taking it off [...] and [he was missing] one boot, indicating also that he had attempted to strip.' Trelawny also relates a supposed deathbed confession by an Italian fisherman who claimed to have rammed Shelley's boat in order to rob him, a plan confounded by the rapid sinking of the vessel. Shelley's body washed ashore and later, in keeping with quarantine regulations, was cremated on the beach near Viareggio. Also, Trelawney, in his account of the recovery of Shelley's body, records that "the face and hands, and parts of the body not protected by the dress, were fleshless," and by the time that the party returned to the beach for the cremation, the body was even further decomposed. In his graphic account of the cremation, he writes of Byron being unable to face the scene, and withdrawing to the beach.

Shelley's heart was snatched from the funeral pyre by Edward Trelawny; Mary Shelley kept it for the rest of her life, and it was later buried with the body of Sir Percy Florence Shelley, their son. Shelley's ashes were interred in the Protestant Cemetery, Rome under an ancient pyramid in the city walls. His grave bears the Latin inscription, Cor Cordium ("Heart of Hearts"), and, in reference to his death at sea, a few lines of "Ariel's Song" from Shakespeare's The Tempest: "Nothing of him that doth fade / But doth suffer a sea-change / Into something rich and strange." The grave site is the second in the cemetery. Some weeks after Shelley had been put to rest, Trelawny had come to Rome, had not liked his friend's position among a number of other graves, and had purchased what seemed to him a better plot near the old wall. The ashes were exhumed and moved to their present location. Trelawny had purchased the adjacent plot, and over sixty years later his remains were placed there.

Shelley was eventually memorialized at the Poets’ Corner at Westminster Abbey, along with his old friends, Lord Byron and John Keats.