Percy Bysshe Shelley was born 4 August 1792 at Field Place, near Horsham, Sussex, England. The eldest son of Timothy and Elizabeth Shelley, he stood in line to inherit his grandfather’s considerable estate and a seat in Parilament. He attended Eton College, where he began writing poetry, and went on to Oxford University. His first publication was a Gothic novel, Zastrozzi (1810), in which he voiced his own heretical and atheistic opinions through the villain Zastrozzi. After less than a year at Oxford, he was expelled for writing and circulating a pamphlet promoting atheism.
At 19, Shelley eloped to Scotland with 16-year-old Harriet Westbrook. Two years later he published his first long serious work, Queen Mab: A Philosophical Poem. The poem emerged from Shelley’s friendship with the British philosopher William Godwin, and it expressed Godwin’s freethinking socialist philosophy. Shelley also fell in love with Godwin and Mary Wollstonecraft’s daughter, Mary, and in 1814 they eloped to Europe. In 1815 the couple went to Lake Geneva, where Shelley spent a great deal of time with the poet Lord Byron, sailing on Lake Geneva and discussing poetry and the supernatural late into the night. The same year, Shelley wrote the verse allegory Alastor, or The Spirit of Solitude. In December 1816 Harriet Shelley apparently committed suicide. In a matter of weeks, Shelley and Mary Godwin were officially married.
Early in 1818, Percy and Mary Shelley left England for the last time, and went to Italy. During the remaining four years of his life, Shelley produced all his major works, including The Masque of Anarchy, written in response to the Peterloo Massacre of 1818, The Cenci and Prometheus Unbound. On 8 July 1822, shortly before his 30th birthday, Shelley was drowned in a storm while attempting to sail from Leghorn to La Spezia, Italy, in his schooner, the Don Juan.
Further information about the life of Percy Shelley can be found here via the Oxford Dictionary of National Biography.