In 1931 Paris, 12-year-old Hugo Cabret lives with his widowed, clockmaker father, who works at a museum. Hugo’s father finds a broken automaton – a mechanical man created to write with a pen. He and Hugo try to repair it, documenting their work in a notebook. When his father dies in a fire, Hugo goes to live with his father’s alcoholic brother, uncle Claude, who maintains the clocks at Gare Montparnasse railway station. When Claude goes missing, Hugo continues maintaining the clock, fearing that Station Inspector Gustave Dasté will send him away if Claude’s absence is discovered. Hugo attempts to repair the automaton with stolen parts, believing it contains a message from his father, but the machine requires a heart-shaped key.
Hugo is caught stealing parts from a toy store, and the owner, Georges, takes his notebook, threatening to destroy it. Georges’ goddaughter Isabelle offers to help Hugo get the notebook back, by working at his toy store, as an assistant. In addition to his job working maintaining the clocks. Isabelle and Hugo become fast friends, and Hugo is astonished to see Isabelle wears a heart-shaped key, given to her by Georges. Hugo shows her the automaton, which they activate with the key, and the machine draws a scene from the film A Trip to the Moon, once described to Hugo by his father. Isabelle identifies the drawing’s signature as that of “Georges Méliès”, her godfather. She sneaks Hugo into her home, where they find a hidden cache of drawings, but they are discovered by Georges.
Several days later, at the Film Academy Library, Hugo and Isabelle find a book about the history of cinema that praises Méliès’ contributions. They meet the book’s author, René Tabard, a film expert who is surprise to hear Méliès is alive, as he disappeared after World War I along with the copies of his films. Excited at the chance to meet Méliès, René agrees to meet Isabelle and Hugo at Georges’ home to show his copy of A Trip to the Moon.
Finding the key on the station railway tracks, Hugo drops down to the track to retrieve it, and is run over by an uncontrollable train that smashes through the station. He wakes up, having only had a nightmare, but hears an ominous ticking emanating from himself, and discovers he has been turned into the automaton. Hugo wakes up again to discover this was only another nightmare.
At Georges’ home, his wife Jeanne allows them in after René compliments her as Jeanne d’Alcy, an actress in many of Méliès’ films. They play the film, waking Georges, who is finally convinced to cherish his accomplishments rather than regret his lost dream. Georges recounts that as a stage magician, he was fascinated by motion pictures, and used film to create imaginative works through his Star Film Company. Forced into bankruptcy after the war, he closed his studio and sold his films. He laments that even an automaton he built and donated to a museum was lost, which Hugo realizes is the one he has repaired.
Hugo races to the station to retrieve the automaton, but is caught by Gustave, who has learned that Claude’s body was found. Gustave threatens to take Hugo to the orphanage, and Hugo runs away but drops the automaton on the tracks. He jumps down to retrieve it and is almost run over by a train, but Gustave saves him and the automaton. Georges arrives, and tells Gustave, “This boy belongs to me”.
Some time later, Georges is named a professor at the Film Academy, and is paid tribute through a showcase of his films recovered by René. Hugo and his new family celebrate at the apartment, and Isabelle begins to write down Hugo’s own story.