In the mid-19th century, P. T. Barnum and his troupe perform a show at the circus ("The Greatest Showman.)
As a child, Barnum and his tailor father Philo work for the Hallett family. He becomes infatuated with their daughter Charity and we see him making her laugh. Though Charity is being sent to finishing school, Barnum reassures her that they will not be separated. The two keep in touch through letters until they meet again in adulthood eventually marrying and raising two daughters, Caroline and Helen, in New York City. They live a humble life; though Charity is happy, Barnum craves more.
Barnum loses his job as a clerk at a shipping company after the company goes bankrupt, and returns home for Caroline's birthday. In a daring risk, he takes out a large loan from a bank, deceiving them into accepting his former employer's lost ships as collateral. He uses this loan to set up Barnum's American Museum in downtown Manhattan, an attraction showcasing various wax models. Initially, sales are slow. On the suggestion of his children to showcase something "alive", Barnum searches for "freaks" to serve as performers for his museum. He gathers a large group of them including Lettie Lutz. This attracts a large audience despite protests and poor reviews from James Gordon Bennett, prompting Barnum to rename his venture "Barnum's Circus".
Searching for ways to further his reputation amongst the upper class, Barnum meets playwright Phillip Carlyle and convinces him to join his venture.Carlyle is mesmerized by the African American trapeze artist Anne Wheeler, but he hides his feelings. During a trip, Carlyle arranges for Barnum and his troupe to meet Queen Victoria. Afterwards, Barnum meets famed Swedish singer Jenny Lind, whom he convinces to perform in America with him serving as her manager. Lind's first American performance is a rousing success during the song, Carlyle and Wheeler are spotted by Carlyle’s parents as they are holding hands. As Barnum gains favor with the aristocratic patrons, he begins to distance himself from his troupe as he advises them to work on that night's show. Dejected, they decide to stand against their local harassers.
Carlyle and Wheeler attend the theatre together one night only to run into Carlyle’s parents, who chastise Carlyle for "parading around with the help". Wheeler runs off, and Carlyle angrily
berates them, then chases Wheeler and tries to convince her that they can be together, but she rejects him despite her feelings for him . As Barnum takes Lind on a US tour, Charity feels isolated from her husband as she stays home with their daughters. While on tour, Lind begins falling in love with Barnum. When he refuses her advances, she threatens to quit and orchestrates a kiss with him at the end of her last show, which is photographed by the press.
Barnum returns home to find his circus on fire, caused by a fight between the protesters and the troupe. Carlyle runs into the burning building, believing that Wheeler is still inside, and suffers serious injuries before being rescued by Barnum. Barnum gets word from a sympathetic Bennett that the culprits have been caught and that Lind has canceled her tour after her and Barnum's "scandal". Barnum's mansion is foreclosed upon and Charity takes their daughters to her parents' home.
Devastated by his selfishness, Barnum retreats to a local bar where his troupe find him and explain that despite their disappointments, they still consider themselves a family that needs him. An inspired Barnum resolves to start a new show and not let ambition overtake his loved ones anymore. Carlyle wakes in a hospital with Wheeler by his side. Barnum finds Charity and they mend their relationship.
Barnum is faced with the financial difficulty of rebuilding the circus, but the recovering Carlyle steps in, offering to use his share of the circus's profits to rebuild it under condition of becoming a full partner, which Barnum happily accepts. To save money, Barnum transforms the enterprise into an open-air tent circus by the docks.
The revamped circus is a huge success. Barnum gives full control of the show to Carlyle to spend more time with his family.