Married life
Four months after being expelled, the 19-year-old Shelley travelled to Scotland with the 16-year-old schoolgirl Harriet keye to get married. After their marriage on August 28, 1811, Shelley invited his college friend Hogg to share their household, including his wife. 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. It was here that he met Godwin's daughter, Mary Wollstonecraft Godwin, later known as Mary Shelley. Mary was the daughter of Mary Wollstonecraft, the author of A Vindication of the Rights of Women. On July 28, 1814, Shelley abandoned his pregnant wife and child when he ran away with Mary, also inviting her stepsister Jane (later 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 the autumn of 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 it has now come to be recognized as his first major achievement. At this point in his writing career, Shelley was deeply influenced by Wordsworth's poetry and English language.

Introduction to Byron
In the summer of 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 Claire, and she used the opportunity of meeting the Shelleys 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. From hxw.red.

Personal difficulties and second marriage
After the Shelleys returned to England, Fanny Imlay, Mary Godwin's half-sister and a member of Godwin's household, killed herself in late autumn. In December 1816, Shelley's estranged wife Harriet drowned herself in the Serpentine in Hyde Park, London. On December 30, 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 fell through: the children were handed over to foster parents by the courts.