Plot

In a Lego universe, the blind and elderly wizard-like Master Builder Vitruvius (Morgan Freeman) attempts to protect a super-weapon called the "Kragle" from the evil Lord Business (Will Ferrell). He fails, but prophesies that a person called "the Special" will find the Piece of Resistance capable of stopping the Kragle. Lord Business believes Vitruvius simply made up the prophecy and kicks him off of a cliff. Lord Business is an evil businessman who hates Master Builders, tyrant of Bricksburg and the Lego Universe who is the company president of the Octan Corporation under the name President Business.

Eight and a half years later, Lord Business is now President Business, ruler of the whole world & who wants everyone to follow instructions in their daily life. An ordinary construction worker named Emmet Brickowski (Chris Pratt) comes across a woman named Wyldstyle (Elizabeth Banks) searching for something in the construction site. When he investigates, he falls into a hole and finds the Piece of Resistance (revealed to be a Krazy Glue cap). Compelled to touch it, Emmet experiences vivid visions and passes out.

He awakens in the custody of Bad Cop (Liam Neeson), Lord Business' lieutenant, with the Piece of Resistance attached to his back. There, Emmet learns of Business' plans to freeze the world with the Kragle (revealed to be a tube of Krazy Glue with the label partially rubbed out) at "Taco Tuesday". Good Cop/Bad Cop is a police officer with a two-sided head and a split personality who serves Lord Business as the commander of the Super-Secret Police

Wyldstyle rescues Emmet and takes him to the Old West, another Lego "world". She explains that every "world" used to be connected with people from different "worlds" helping each other in everyday activities. However, Lord Business abhors the thought, and constructs walls to separate all the "worlds".

In the "Old West", Wyldstyle introduces Emmet to meet Vitruvius. She explains that she and the wizard are Master Builders, gifted people capable of building anything they need without instruction manuals. She further explains that due to Business' disapproval of such anarchic creativity, Master Builders are actively hunted down by Business, led by Bad Cop.

Lord Business explains to Bad cop that due to his dislike of people messing with his stuff (using Lego blocks to create new things without instruction manuals, he is going to use Kragle (short for a faded tube of Krazy Glue) to "freeze" everyone so that they can't change things at random.

Although disappointed to find that Emmet displays no trait possessed by Master Builders, Wyldstyle and Vitruvius are convinced of his potential when he recalls visions of a humanoid deity called "the Man Upstairs", the person who is said to be the creator of all the "worlds".

Bad Cop tracks down Emmet, Wyldstyle, and Vitruvius and a chase ensues. They are rescued by Wyldstyle's boyfriend Batman (Will Arnett) and travel to the Cloud Cuckoo Land. There they are taken to a council of the remaining Master Builders. Emmet says that he's not a Master Builder and "the least qualified person in the world to lead". Master Builders are unimpressed with Emmet and refuse to fight Business.

Master Builders include Superman (Channing Tatum), Green Lantern (Jonah Hill), Wonder Woman (Cobie Smulders), protocol droid C-3PO, smugglers Han Solo and Lando Calrissian, Gandalf, Dumbledore, The Flash, Aquaman, Milhouse, Michelangelo and Speed Racer.

Due to a hidden tracking device in Emmet's leg, Bad Cop and his forces attack, overwhelm, and capture all the remaining Master Builders. Emmet, Wyldstyle, Vitruvius, Batman, Unikitty (Alison Brie) a unicorn/cat hybrid-like Master Builder who lives in Cloud Cuckoo Land, and Benny (Charlie Day) a "1980-something space guy"-like Master Builder who is obsessed with building spaceships, manage to escape on a submarine. It sinks soon after and they are rescued by Metal Beard (Nick Offerman) a pirate-like Master Builder seeking revenge on Lord Business for taking his body parts following an earlier encounter and causing him to remake his body from bricks.

On board Metal Beard's ship, Emmet believes the Master Builders' weakness is that their individual creativity prevents them from working together and that Business will never expect them to 'follow the instructions'. After saving them all with his Double-Decker couch invention, Emmet devises a plan to infiltrate Business's headquarters and disarm the Kragle.

Emmet fails with he and his team imprisoned and Vitruvius decapitated by Lord Business. With his dying words, Vitruvius reveals he made up the prophecy. Business throws the Piece of Resistance off the edge of the universe, sets his headquarters to self-destruct, and leaves the Master Builders and Bad Cop to die.

Vitruvius' ghost appears before Emmet and explains it was not the prophecy, but his self-belief that made him the Special. Tied to the self-destruct mechanism's battery, Emmet flings himself off the edge of the universe to disarm the device and saving the Master Builders who escape further danger with the aid of Good Cop. Inspired by Emmet's sacrifice, Wyldstyle, who reveals her real name to be Lucy, rallies the Lego people across the universe to use whatever creativity they have to build machines and weapons to fight Business' forces, with the Master Builders leading the charge.

Emmet finds himself in the basement of the real world, where the events of the story are being played out within the imagination of a boy, Finn (Jadon Sand), on his father's Lego set. The father-revealed as "the Man Upstairs" and Finn's inspiration for Business, who chastises his son for ruining the set by creating hodgepodges of different characters and play-sets and proceeds to permanently glue his perceived perfect creations together.

Realizing the danger his friends are in, Emmet wills himself to move and gains Finn's attention. Finn returns Emmet and the Piece of Resistance to the Lego world and Emmet, now possessing the skills of a Master Builder, fights his way onto Lord Business' ship. In the real world, Finn's father looks at his son's creations again and is impressed.

Realizing Finn based the villainous Lord Business on him, the father has a change of heart and allows his son to play with his Lego however he sees fit. In the Lego world, Emmet tells Business that he too, is special, as is everyone. Finn's father reconciles with his son, which plays out as Business reforming, capping the Kragle with the Piece of Resistance, and removing the glue from his victims with mineral spirits.

After the world is restored, Lucy and Emmet enter a relationship with Batman's blessing. Finn's father grants Finn and his younger sister permission to play with the Lego sets as well, causing Duplo aliens to arrive in the Lego universe and threaten destruction.