Thomas "Tom" Natsworthy is the main protagonist of the Mortal Engines Quartet.
Sometime before the events of the series, a tier imbalanced and crushed his home and his parents (an event known as The Big Tilt), making him an orphan. He was adopted by the Historians Guild, who let him help in the museum.London is chasing the town of Salthook, Tom gets into a fight with a fellow apprentice who was bullying him because of his parents. As punishment, Tom is sent down to London's Gut for the night to make sure that no historical artefacts are destroyed. While he is down there, he sees Katherine Valentine, whom he instantly falls in love with. A veiled girl then attempts to assassinate Thaddeus Valentine. However, Tom sees the knife and stops her from stabbing him. She runs away with Tom in pursuit. When he asks her why she tried to kill Valentine she screams "ASK HIM! ASK HIM WHAT HE DID TO HESTER SHAW!" before jumping overboard. When Thaddeus and the engineers come up to see what has happened, Tom tells them about what she said. Thaddeus Valentine pushes him off London to the ground below. He lands in mud and survives. He meets with Hester Shaw. He finds it hard to believe that he was pushed, and wonders if he fell by accident. He and Hester follow London with the hope of being rescued again, but London drives relentlessly on into the distance. Soon they are picked up by the town of Speedwell and think they have been rescued. However, they are locked up and are prepared to be sold as slaves at the Trading Cluster. However, they are rescued by Anna Fang. They escape the Trading Cluster aboard the Jenny Haniver. Aboard, Anna asks Tom about what life was like in London. Tom tells the Aviator enthusiastically, who listens intently. On the way they see the Rust-Water Marshes and the rusted wreak of a starved traction city that is getting slowly stripped down by scavenger towns. At last they arrive at the flying town of Airhaven. Tom is amazed to be at the famous town. They land, but do not notice the London airship that has also landed. They enter a cafe called The Gasbag and Gondola, and while they are there, Shrike arrives and attempts to kill him and Hester. They escape while Anna fights Shrike in a Hot Air Balloon and fly away from Airhaven. When the balloon lands, Shrike finds Tom and Hester again, and while the pirate suburb Tunbridge Wheels chases a town, it runs over Shrike. Tom is shoved aboard the suburb with Hester and they are captured by the pirates. While he and Hester are locked in the suburb's gut, Tom yells at the pirate mayor Chrysler Peavy that he is a coward. Peavy recognizes Tom's accent and is pleasured that he has a London citizen aboard his suburb. Peavy invites Tom and Hester to the town hall and asks Tom if he will help Tunbridge Wheels become a decent city like London. Tom unwillingly agrees, and Tunbridge Wheels floats across the Sea of Khazak to eat Airhaven, which is resting on the Black Island. Tom and Hester and Peavy are forced to row in a boat towards the island because Tunbridge Wheels was sunk by Anna Fang's Jenny Haniver. After Peavy drowns in mud, Shrike finds Tom and Hester again, and Tom kills Shrike by stabbing him with a sword. Anna Fang then finds him and Hester and they go to Batmunkh Gompa. While wandering the streets of Batmunkh Gompa, Tom sees Thaddeus Valentine disguised as a monk. Tom tells Anna Fang and she duels Valentine and is stabbed by him. Tom tells Anna Fang that she beat him, she dies. Tom and Hester then inherit the Jenny Haniver and they fly off to London. Tom drops off Hester in London and Tom and the Jenny Haniver are attacked by Valentine's 13th Floor Elevator. Tom shoots rockets at the Elevator's windows, killing its crew. The airship crashes down onto London and Tom goes to rescue Hester, Thaddeus Valentine, and the dying Katherine Valentine. Valentine tells Tom and Hester to save themselves, and Tom flies the Jenny Haniver away from London, which is destroyed by MEDUSA moments later. Tom is devastated by the death of London and Katherine, but realizes that he really loves Hester and not Katherine. So he flies the Jenny away so he and Hester can begin their life on The Bird Roads.
Tom and Hester travel the world for two years, and are in Airhaven when they meet writer and Professor Nimrod Pennyroyal. Pennyroyal asks Tom and Hester if he could accompany them on the Jenny Haniver, and Tom agrees. While flying, the airship is attacked by Fox Spirits, airships of the Green Storm. Tom steers the Jenny through the tiers of a city (an idea he learned from Valentine) and escapes the Fox Spirits, and end up flying through The Ice Wastes. There they come across the trading city of Anchorage and are welcomed by the margravine Freya Rasmussen, who later has a crush on Tom. Tom starts spending time with Freya Rasmussen more than he does with Hester, who later witnesses Tom and Freya kissing. When Hester flies to Arkangel in the Jenny Haniver, Tom is awoken in his sleep by Caul, one of the Lost Boys who was spying on him. Tom follows Caul and finds that the Jenny is gone, and is then captured by the Lost Boys and taken aboard the limpet 'The Screw Worm, where he is taken to the sunken raft city of Grimsby, home of the Lost Boys. He meets Uncle, the leader of the Lost Boys, who tells Tom that Hester is at Rogues' Roost, an island near Greenland. Tom is abandoned by the Lost Boys and is attacked by Stalker-Birds when he arrives, and he finds Hester. Before he and Hester escape the island, Tom meets the Stalker Fang, the resurrected form of Anna Fang. The stalker recognizes Tom, and she doesn't kill him. They escape Rogues' Roost and go back to Anchorage, which is then being chased by Arkangel. After Arkangel sinks, Tom then realizes that Pennyroyal's books are lies, and when he tries to find him, he sees Pennyroyal trying to escape in the Jenny Haniver. Pennyroyal accidentally shoots Tom in the chest with a pistol, saying that he only meant to scare Tom. Pennyroyal then steals the Jenny Haniver and leaves the injured Tom. He is taken to Anchorage's hospital and the bullet shot as his heart was removed surgically. When Anchorage lands in the green lands of Vineland, Tom and Hester stay at Anchorage, and Tom would later find out that Hester is pregnant.
In the static city of Anchorage-In-Vineland, Tom and Hester have been married for sixteen years and have a daughter; Wren Natsworthy. Tom's heart still aches from the bullet shot by Pennyroyal. When Wren is captured by the Lost Boys, Tom, Hester, Freya, and Caul go aboard the Screw Worm to find her. They visit Grimsby, which is now falling apart and are locked up by Uncle. Caul helps them escape, and Tom and Hester take the Screw Worm to the raft city of Brighton while Caul and Freya go back to Anchorage. Tom is captured in Brighton and becomes a slave. Hester frees him, Tom promises to help the Lost Boy Fishcake, but who they later abandon when they steal back the Jenny Haniver. They find Wren, her friend Theo Ngoni, and Pennyroyal, now the mayor of Brighton. Finally, Hester admits to Tom that she sold Anchorage to Arkangel. Tom is stunned when he hears this, and Hester leaves him so she can live with the re-resurrected Shrike. Tom, Wren, Theo, and Pennyroyal then escape Brighton in the Jenny Haniver.
Six months after Hester left Tom in Brighton, Tom visits a doctor in Peripetiapolis, and finds out that the wound from Pennyroyal's bullet would soon prove fatal. He later sees a woman who he believes to be Clytie Potts, a Historian from London. He asks her who she is and she claims that her name is Cruwys Morchard.
Tom Natsworthy is described as a scrawny, thin young boy in Mortal Engines. In Predator's Gold he is said to be handsome and slightly older. However in the last two books he is described as a middle-aged man whose hair seems to be thinning. It is also noted that he is not described as handsome anymore although Hester Shaw and Stalker Fang do bring up Tom's past Good looks.