At sixteen, Claire Clairmont was a lively, voluptuous brunette with a good singing voice and a hunger for recognition. Her home life had become increasingly tense, as her stepfather William Godwin sank deeper into debt and her mother's relations with Godwin's daughter Mary Shelley became more strained. Clairmont aided her stepsister's clandestine meetings with Percy Bysshe Shelley, who had professed a belief in free love and soon left his own wife and two small children to be with Mary. When Mary ran away with Shelley in July 1814, Clairmont went with them. Clairmont's mother traced the group to an inn in Calais, but couldn't make Clairmont go home with her. Godwin needed the financial assistance that the aristocratic Shelley could provide.
Clairmont remained in the Shelley household in their wanderings across Europe. The three young people traipsed across war-torn France, into Switzerland, fancying themselves like characters in a romantic novel, as Mary Shelley later recalled, but always reading widely, writing, and discussing the creative process. On the journey, Clairmont read Rousseau, Shakespeare, and the works of Mary's mother, Mary Wollstonecraft. "What shall poor Cordelia do – Love & be silent," Clairmont wrote in her journal while reading King Lear. "Oh [th]is is true – Real Love will never [sh]ew itself to the eye of broad day – it courts the secret glades." Clairmont's emotions were so stirred by Cordelia that she had one of her "horrors", a hysterical fit, Mary Shelley recorded in her own journal entry for the same day. Clairmont, who was surrounded by poets and writers, also made her own literary attempts. During the summer of 1814, she started a story titled 'The Idiot', which has since been lost. In 1817–18, she wrote a book which Percy Bysshe Shelley tried without success to have published. Although Clairmont lacked the literary talent of her stepsister and brother-in-law, she always longed to take centre stage. It was during this period that she changed her name from "Jane" to first "Clara" and finally the more romantic-sounding "Claire".
Any romantic designs Clairmont might have had on Shelley were frustrated initially, but she did bring the Shelleys into contact with Lord Byron, with whom she entered into an affair before he left England in 1816 to live abroad. (A year marked by agricultural failures and widespread European famine, but also of significant literary advances as the Godwin-Shelley-Byron circle holed up indoors, 1816 would later be known as the "year without a summer".) Clairmont had hopes of becoming a writer or an actress and wrote to Byron asking for "career advice" in March 1816, when she was almost eighteen. Byron was a director at the Drury Lane Theatre. Clairmont later followed up her letters with visits, sometimes with her stepsister Mary, whom she seemed to suggest Byron might also find attractive. "Do you know I cannot talk to you when I see you? I am so awkward and only feel inclined to take a little stool and sit at your feet," Clairmont wrote to Byron. She "bombarded him with passionate daily communiques" telling him he need only accept "that which it has long been the passionate wish of my heart to give you". She arranged for them to meet at a country inn. Byron, in a depressed state after the break-up of his marriage to Annabella Milbanke and scandal over his relationship with his half-sister Augusta Leigh, made it very clear to Clairmont before he left that she would not be a part of his life. Clairmont, on the other hand, was determined she would change his mind.
She convinced Mary and Percy Shelley that they should follow Byron to Switzerland, where they met him and John William Polidori (Byron's personal physician) at the Villa Diodati by Lake Geneva. It is unknown whether or not Clairmont knew she was pregnant with Byron's child at the commencement of the trip, but it soon became apparent to both her travelling companions and to Byron not long after their arrival at his door. At first he maintained his refusal of Clairmont's companionship and allowed her to be in his presence only in the company of the Shelleys; later, they resumed their sexual relationship for a time in Switzerland. Clairmont and Mary also made fair copies of Byron's work-in-progress, 'Childe Harold's Pilgrimage', which he was in the process of writing.
Clairmont was the only lover, other than Caroline Lamb, whom Byron referred to as a "little fiend". Confessing the affair in a letter to his half-sister Augusta Leigh, Byron wrote: "What could I do? – a foolish girl – in spite of all I could say or do – would come after me – or rather went before me – for I found her here... I could not exactly play the Stoic with a woman – who had scrambled eight hundred miles to unphilosophize me."
He referred to her also in the following manner, in a letter to Douglas Kinnaird (20 January 1817): "[Claire Clairmont] You know – & I believe saw once that odd-headed girl – who introduced herself to me shortly before I left England – but you do not know – that I found her with Shelley and her sister at Geneva – I never loved her nor pretended to love her – but a man is a man – & if a girl of eighteen comes prancing to you at all hours of the night – there is but one way – the suite of all this is that she was with child – & returned to England to assist in peopling that desolate island... This comes of "putting it about" (as Jackson calls it) & be dammed to it – and thus people come into the world."
Clairmont was to say later that her relationship with Byron had given her only a few minutes of pleasure, but a lifetime of trouble.
The group left Byron in Switzerland at the end of the summer and returned to England. Clairmont took up residence in Bath and in January 1817 she gave birth to a daughter, Alba, whose name was eventually changed to Allegra. Throughout the pregnancy, Clairmont had written long letters to Byron, pleading for his attention and a promise to care for her and the baby, sometimes making fun of his friends, reminding him how much he had enjoyed making love to her, and sometimes threatening suicide. Byron, who by this time hated her, ignored the letters. The following year, Clairmont and the Shelleys left England and journeyed once more to Byron, who now resided in Italy. Clairmont felt that the future Byron could provide for their daughter would be greater than any she herself would be able to grant the child and, therefore, wished to deliver Allegra into his care.
Upon arriving in Italy, Clairmont was again refused by Byron. He arranged to have Allegra delivered to his house in Venice and agreed to raise the child on the condition that Clairmont keep her distance from him. Clairmont reluctantly gave Allegra over to Byron.
Clairmont was granted only a few brief visits with her daughter after surrendering her to Byron. When Byron arranged to place her in a Capuchin convent in Bagnacavallo, Italy, Clairmont was outraged. In 1821, she wrote Byron a letter accusing him of breaking his promise that their daughter would never be apart from one of her parents. She felt that the physical conditions in convents were unhealthy and the education provided was poor and was responsible for "the state of ignorance & profligacy of Italian women, all pupils of Convents. They are bad wives & most unnatural mothers, licentious & ignorant they are the dishonour & unhappiness of society ... This step will procure to you an innumerable addition of enemies & of blame."
By March 1822, it had been two years since she had seen her daughter. She plotted to kidnap Allegra from the convent and asked Shelley to forge a letter of permission from Byron. Shelley refused her request. Byron's seemingly callous treatment of the child was further vilified when Allegra died there at age five from a fever some scholars identify as typhus and others speculate was a malarial-type fever. Clairmont held Byron entirely responsible for the loss of their daughter and hated him for the rest of her life. Shelley's death followed only two months later.