Eustace Scrubb was born in 1933 to Harold and Alberta Scrubb. He grows up an only child, very spoiled and modern. In the summer of 1942 (2306 NT) when his cousins Edmund and Lucy Pevensie are visiting him, they are swept into Narnia through a painting on the wall of Lucy's bedroom.
There, they are found by King Caspian X and his crew on their journey to the world’s end, and joins them. Eustace hates being in Narnia and doesn't try to understand it and makes himself a nuisance, being unkind to the talking animals and attempting to steal water during rationing.
At one of the islands, Eustace runs away from the party of workers and gets lost, spending the night in the cave of a dragon. When he awakes, he discovers he had turned into a dragon. He is a dragon for several weeks, until Aslan appears to him and turns him back into a boy. During his transformation, Eustace learns to love and be loved. He journeys with the others to the World’s End, where he leaves the ship with his cousins and Reepicheep the Mouse and goes on. After Reepicheep leaves them, the three humans met Aslan, who sends them back into their own world.
Later that year at school, he and his friend Jill Poll escapes to Aslan's Country through a garden gate while being pursued by school bullies. When trying to save Jill from falling over a high cliff, Eustace himself falls in, but is caught by the breath of Aslan and is blown to Narnia. After Jill follows him there, she tells him that Aslan had met her and had given them three signs to help them find the missing prince of Narnia. Because Eustace does not recognize an older Caspian immediately upon arriving in Narnia, they miss the first sign but do find some allies in the Owls who promise to aid them.
They met up with the marshwiggle Puddleglum, who joins them on their quest, and they begin to travel North. While traveling in the northern territory of the Giants, a lady tells them of the Gentle Giants of Harfang and directs them to the Giant's city, where the travelers go to flee a winter storm. While there, they muff the second and third sign, and must escape from the Giants when they realize them mean to eat them. While being pursued, they manage to fall into what is the entry to the Underground World, where they are captured by the Underworlders and taken a long distance to the Queen's city.
There they meet a strage Prince, who later reveals himself to be the missing Prince Rilian under an enchantment. Eustace is pivitol in freeing Rilian from his enchantment, and aids in killing the Lady of the Green Kirtle. Once this is done, the group of Narnians travel until they find an opening into the Overworld, which leads them directly to Narnia. There, Rilian is united with his dying father Caspian, and Eustace and Jill are sent back to Aslan's Country, where they witness Caspian's arrival to Aslan's Country, and aid Aslan in teaching the school bullies a lesson.
In 1949 (2555 NT), at the age of 16, Eustace meets with the Seven Friends of Narnia. They are surprised with a man appears to them who has a "Narnian look about him" and they agree that Jill and Eustace must go to Narnia. While on the train back to school, and "sudden jerk" throws Jill and Eustace into Narnia, where they meet the man they had seen with the other Friends of Narnia. The man introduces himself as King Tirian of Narnia and asks Jill and Eustace to aid him in undoing the lies that are destroying Narnia.
Eustace and Jill do all they can, but are eventually defeated by the Calormenes and are thrown into the Stable. There, Eustace finds himself reunited with the rest of the Friends of Narnia and Narnians in Aslan's Country, and witnesses the end of Narnia. Later, after he is counted among the faithful at the Great Reunion, he is told by Aslan that he had died in a railway crash in England, and would be staying in the New Narnia forever.