Lucy is the youngest Pevensie, was sent with her other siblings to live with Professor Kirke in the country when she was eight, to escape the bombing of London. There she discovered the door to Narnia in a magic wardrobe during an impromptu tour of the house. Once in Narnia, she meets Mr. Tumnus the faun, and is taken to his cave for tea. Only later does she learn that he had planned to kidnap her and give her to the White Witch. Tumnus' good side wins out, however, and he helps Lucy to get back to the wardrobe safely. Once back in England, Lucy can't wait to tell the others of her discovery, and is crushed when no one believes her.
Lucy traveled through the Wardrobe two more times; once with Edmund during a hide-and-seek game, and once with the rest of the Pevensies when they were hiding from Mrs. Macready.
During their latest trip, Lucy visited Tumnus' cave along with the others but discovered that it has been ransacked and the faun captured by the WW's secret police. Outside the cave they meet Mr. Beaver, who presents Lucy's handkerchief as a token of friendship and takes them to his dam where he tells them what happened to Tumnus, and that only Aslan can help him.
After Edmund disappears, group hides from the wolf pack and later meets Father Christmas, who has been able to come back now that winter is weakening from Aslan's return. Father Christmas gives Lucy a dagger and a cordial made from the juice of the fire-flowers that cures any injury.
A bit after they arrive at Aslan's camp, Lucy and Susan are present at the killing and resurrection of Aslan. They accompany him to the WW's castle, where he revives the stone statues, including Lucy's friend Tumnus. From there they travel to the battle at Beruna, where Aslan kills the White Witch, and Lucy heals Edmund with her cordial. She is later crowned Queen Lucy the Valiant, and reigns for 15 years.
In 1014 NT, Lucy journeys to Archenland along with King Edmund and a group of Narnians, and aids them as an archer in a Calorman attack on Archenland. Not too long after, Lucy returns to England along with her siblings when they stumble back through the wardrobe while on a hunting trip.
She returns to Narnia a year later (2303 NT), when Caspian blows Queen Susan's Horn and summons them back. Arriving at the ruin's of Cair Paravel, they meet up with Trumpkin and travel through the forests of Narnia to reach Caspian. Lucy spots Aslan during their trip, and is crushed when no one believes her. She is reunited with Aslan later that day, and while Peter and Edmund continue to go to Caspian's aid, Susan and Lucy remain with Aslan and assists him in restoring the Old Narnia and awakening the trees. After the Second Battle of Beruna, Caspian is crowned king and the Pevensies return to England.
Six months later (2306 NT), while staying at the house of their relatives for the summer, Lucy, Edmund and their cousin Eustace are sucked back into Narnia through a picture of a Narnian ship on Lucy's bedroom wall. They arrive on the Dawn Treader, a ship of Narnians lead by Caspian, journeying to the Worlds End. Their first stop is at the Lone Islands, where the group is captured by slave traders and are only rescued after Caspian is sold and then reveals his identity. From there they journey through a terrible storm which blows them to Dragon Island, where Lucy comforts Eustace when he is turned into a dragon, and rejoices when he is restored.
From there they travel to Deathwater Island and then to the Land of the Duffers, where Lucy is instrumental in lifting an invisible spell that is on the Island's unusual inhabitants, the Dufflepuds.
After their task is completed there, they continue sailing on, past the Dark Island, until they beginning of the end of the world, known as Ramandu's Island. From there, as the final part of the quest, they embark on the last leg of the voyage, in which they attempt to sail as far east as the ship will allow.
When they finally reach shallow water, Lucy, Edmund and Eustace board a small boat and drift along until they reach land, which they learn is Aslan's Country. There they meet Aslan, who tells Lucy and Edmund that they can no longer return to Narnia because they are too old. They then return home.
Lucy lives a full and happy life, but died in a railroad accident at the age of 17. She was able to enter Aslan's Country for good, and there she witnessed the ending of Narnia, and later enjoyed a happy reunion with all her old Narnian friends.