Later in life, she had a boyfriend, Thomas, and worked a minimum wage job at a fast-food restaurant. She soon learned that she was pregnant, and Thomas convinced her to keep the baby. However, he got cold feet and walked out on Claire. Claire visited a psychic, Richard Malkin, who told her that only she must raise her child. Claire visited her mother in the hospital and told her she was giving her baby up for adoption, while also tearfully apologizing for being a difficult child herself. Soon after walking out on signing an agreement to give up her baby, she visited Malkin once more, who told her of a suitable couple living in Los Angeles who could adopt the baby. He gave Claire a ticket for Oceanic Flight 815, which would leave the next day. Weeks after the crash, Claire realizes that Malkin foresaw the plane crash, leaving her with no choice but to raise her child alone.
She is taken to the Staff station, where she is treated by Ethan, who administrates regular doses of vaccine to her and her fetus. He also puts an implant in her that, when activated, will produce symptoms of a specific illness. Ethan takes Claire aside one day and tells her that, once she delivers her baby, she won't be allowed to see it again. A drugged Claire accepts the conditions, but on one particular day of surgery, Alex knocks her out and leads her into the jungle. She encounters Rousseau, who also knocks her out and leaves her near the beach. Locke and Boone find Claire when she stumbles back to the caves after her two-week absence, with no memory of anything that's happened since the plane crash. Slowly her memories begin to return, the first of which being when Charlie gave her peanut butter.
Upon returning, Claire is ignored by the other survivors, who refrain from telling her about Ethan's threats until Shannon informs her. She agrees to serve as bait to capture him against Charlie's wishes. Later, Locke seeks her help in making a cradle for her baby as a birthday gift. Days later, Claire goes into labor, and only Kate, Jin and Charlie are present to help deliver the baby because Jack is back in the caves tending to a badly injured Boone. She is initially unable to calm the baby, until Sawyer's voice provides the solution. Intially she doesn't name the baby, still feeling a slight distachment from planning to give it up for adoption. After Rousseau arrives on the beach with a warning of the Others' imminent arrival, she kidnaps Claire's baby, whom Claire finally names Aaron, and begs Charlie and Sayid to bring him back. She waits at the caves with Sun and Shannon until Charlie and Sayid return with Aaron.
Later, Aaron falls ill, prompting Claire to seek Libby's expertise to help her unblock her repressed memories in order to find a cure for what Claire believes could be a life-threatening illness. Remembering where she was taken by Ethan, she and Kate head into the jungle to search for Rousseau. The three of them then return to the Staff station, only for them to find it completely abandoned and ransacked. Disappointed, the three head back. Before departing, Claire informs Rousseau that her daughter, Alex, helped her and is still alive. Upon returning to the beach, Aaron is well and Claire has recovered all of her lost memories from after her abduction by Ethan.
Charlie later approaches Claire, and gives her some vaccine for her and Aaron, to which she accepts. While at the funeral of Ana Lucia and Libby, Claire clasps Charlie's hand, as a sign of reconciliation. That night, after the implosion of the hatch, she kisses Charlie, rekindling their relationship.
Days later, Claire is surprised by a picnic, provided by Charlie. She is distracted when she spots a flock of gulls flying overhead, and rushes off with an idea. Noticing that the birds are tagged, Claire believes that, if they can catch a bird, they could send a distress message to the outside world.She asks Sun and Jin to help build a net to catch one of the birds, but their attempt is thwarted when Desmond frightens the birds away with gunfire. Claire is angry that Charlie is also showing no support for her rescue plan. She follows Desmond to a rocky cliff, where he gives her a bird. Claire learns of Desmond's visions and of Charlie's expected demise. She comforts Charlie, and the two attach a note to the bird before releasing it. Later, Claire suddenly falls violently ill, due to the now activated implant Ethan put in her during her abduction. Juliet cures the illness as a means of earning the survivors' trust.
When Naomi addresses the camp about the world's perspective of their predicament, Claire expresses outrage that they are considered dead. Later, when Karl arrives the next day with news of the Others' impending arrival, Claire is shocked when Charlie accepts a suicidal mission, but is reassured he will be fine by Hurley. Claire travels with the rest of the camp to the radio tower. On the way, they encounter Ben, who is taken hostage, and Alex, who accompanies the group regardless. Claire is delighted to hear that Charlie has disabled the jamming device blocking all outgoing signals, but is still worried that he has not returned to shore.
Later, Claire is asleep when the barracks fall under attack. One of Keamy's men shoots an RPG at Claire's house. She is still inside her house when it explodes, but Sawyer seems to rescue her with only a few minor injuries. Upon safely leaving the confinements of the barracks and its attackers, Claire decides to go back to the beach with Sawyer and Miles. At several points in the journey Miles stares at Claire in a strange manner, Sawyer defends Claire by telling Miles to stop looking at her. Along the way, Claire is distraught when Miles uncovers the bodies of Rousseau and Karl. When Frank cautions them to hide in the bushes to avoid Keamy, Aaron almost gives away their location, but Claire manages to comfort him before being detected. As Sawyer sets camp for the night, Miles again stares at Claire. She falls asleep and wakes to find her father, Christian, holding Aaron, and proceeds to follow him, abandoning Aaron beneath a tree in the process. Later, when Locke enters Jacob's cabin, he finds Claire sitting inside with Christian, claiming that she is fine where she is, and Aaron likewise. Christian cautions Locke before he leaves that Claire's whereabouts should remain a secret.
At Christian Shephard's memorial service, Carole Littleton (who seems to have awakened from her coma) tells Jack of his relationship to Claire, to which he seems deeply shocked. Afterwards she comments to Kate on Aaron, unaware that it is her own grandson. We also learn that the general public believes that Claire was one of those who died on impact, as claimed by the Oceanic Six.
In "There's No Place Like Home", Claire makes an appearance to Kate in an apparent dream. While caressing her sleeping son, she strongly warns Kate not to take "him" back, which is presumably a warning not to take Aaron back to the island.
There has been fan speculation that de Ravin could make random guest star appearances during the fifth season, but that has not been confirmed by the producers.