Sophie, a young orphaned girl, is lying awake one night with a moonbeam shining in her eyes. She gets up from her bed in the dormitory of the orphanage where she lives to close her curtains and sees a giant coming down the street. She watches as the giant sticks something that looks like a trumpet through the bedroom window of some neighbor children and blows. When the giant turns he sees Sophie and snatches her from her room. The giant takes Sophie to Giant Country where he lives in a cave.

Once there, Sophie learns that the giant is called the Big Friendly Giant (the BFG) because he does not eat people, unlike the nine other giants living in Giant Country. The other giants are much larger and uglier than the BFG and they often bully him. These giants travel nightly to countries around the world to eat people. Sophie isn’t able to go back to the orphanage because the BFG is afraid she’ll tell others about the existence of giants and he’ll be forced to live in a zoo.

The BFG tells Sophie that he often travels to Dream Country to collect dreams, which he places in jars and blows into the windows of children. This is what she saw him doing with the trumpet in her village. He takes her to collect dreams and she finds out he can also catch nightmares. The two devise a plan to mix up a nightmare for the Queen of England to convince her of the existence of giants so that they can stop the giants from ever eating another human being.

Sophie and the BFG deliver the dream to the Queen who treats them very kindly. She orders the Army and the Air Force to follow the BFG to Giant Country to capture the giants. The BFG and Sophie lead the military there and they tie up the giants to bring them back to England where they will live out their lives in captivity.

Upon their return to England, the giants are placed in a huge pit where they will eat nothing but snozzcumbers, a terrible tasting vegetable, for the rest of their lives. The Queen has a huge house built for the BFG and a small cottage built for Sophie. Sophie teaches the BFG how to speak, read, and write better and he becomes an author.