Andrew Ketterley is an eccentric and self-serving man, uncle of Digory Kirke and older brother of Digory's mother Mabel. He lives in London with his older sister Letitia, a hard-working and longsuffering woman who endures a great deal of his nonsense. Uncle Andrew is an irresponsible man who has slowly deadened his conscience over time, until he can no longer sense it. He justifies his actions by claiming that ordinary moral laws do not apply to a magician of his stature.
Long ago Uncle Andrew had a godmother named Mrs. Lefay who was a practitioner magician. Before her death, she had entrusted him with a small sealed box, commanding him to destroy it as soon as possible. Overcome by curiosity and a desire to learn more about magic, Andrew instead embarks on a long quest to discover what the box is, what it contains, and what it could be used for. When he finally opens it, he discovers it is full of dust, and that each individual grain of dust comes from a different world. Using the dust, Uncle Andrew creates Magic rings that will transport an object from our world to another. He spends all of his time up in his study, perfecting the rings and using guinea pigs as test subjects.
Around this time Digory and his very ill mother Mabel come to live with Andrew and Letitia while Digory's father is away in India. Digory never sees his uncle until one day when he and the neighbor girl Polly accidentally stumble into Uncle Andrew's study while exploring the back tunnels of their row of houses. Uncle Andrew, who knew that his rings were working but who was too cowardly to try them himself, tricks Polly into picking up a yellow ring, which transports her to another world. But she does not have a green ring to bring her back, and Digory is forced to go after her.
When they return, Uncle Andrew is astonished to see they have accidentally brought someone else with them: Jadis, a powerful Queen who has destroyed her own world of Charn. He is terribly afraid of her and tries to placate her by catering to her every whim, but this only causes more trouble. When Digory uses the magic rings to get Jadis out of London, Uncle Andrew is transported along with several others to the just-created world of Narnia.
Andrew is fascinated by Narnia and its fast-growing properties, and makes great plans to put it to his own use for monetary gain. He is terrified of Aslan, however, and is unable to understand the speech of Aslan and the Talking Animals. Eventually the Talking Animals try to plant him in the ground, on the mistaken assumption that he is a kind of tree. When Uncle Andrew, Digory, and Polly return to England, Uncle Andrew convinces himself that Jadis had been a lovely woman rather than a merciless tyrant, and even imagines that she found him attractive. But he never again experiments with Magic, and becomes a kinder and less selfish man in time.