It's 7am on a Monday morning in Baltimore, 1962. Tracy Turnblad, a pleasantly plump teenager reflects on how much she loves her city and she loves to dance. She dreams of being a star ("Good Morning Baltimore").
Later that day, Tracy and her friend Penny rush home from high school to catch the latest episode of The Corny Collins Show, a teenage dance TV show ("The Nicest Kids in Town"). Meanwhile, Tracy's mom, Edna, is ironing her neighbors' laundry to earn extra money. Penny's mom, Prudy, arrives to pick up her laundry from Edna. Prudy objects to the girls watching "colored music" performed on the show.
The action shifts to the TV studio were the The Corny Collins Show broadcast has just gone to commercial break. Hunky teen idol Link offers his Council Member ring to vapid teen queen dancer Amber (whose overbearing mother, Velma, is the show's producer).
When the show returns from the break, Corny Collins announces an upcoming live prime-time special, where talent scouts will be on-hand and an election to crown Miss Teenage Hairspray will be held. Tracy, watching the show, is mortified to see that Amber is wearing Link's ring. Corny further announces that they're auditioning a new female dancer for the show. Tracy pleads with her mother to let her audition. Tracy's father, Wilbur, arrives home from work at his novelty gag and joke shop. Edna fears that Tracy will be ridiculed at the auditions, but Wilbur encourages Tracy. Meanwhile, Prudy berates Penny for listening to "race music" as Velma criticizes Amber on her poor dancing. All three girls argue with their mothers ("I'm a Big Girl Now").
Tracy ultimately does attend the auditions, where she literally bumps into Link, initiating a romantic dream sequence ("I Can Hear Bells"), which is interrupted when Tracy is called upon to audition. Velma rejects her due to her weight and because Tracy states that she's in favor of racial integration ("Miss Baltimore Crabs").
The following day at school, Tracy is sent to detention because her monumentally teased hair is blocking other students' view of the blackboard. In the detention hall, an African-American boy named Seaweed teaches Tracy some dance moves.
Soon afterwards, Corny Collins is the guest DJ at the school's sophomore hop ("The Madison"). Corny and Link are immediately impressed by Tracy's dance moves.
The next episode of The Corny Collins Show features a new cast member - Tracy ("The Nicest Kids in Town - Reprise"). During an interview with Corny, Tracy again comes out in favor of racial integration, impressing Corny but horrifying Velma. Amber grows increasingly jealous of the attention Tracy is getting, and, to compound the situation, Corny invites Link to sing a song to Tracy ("It Takes Two"). Tracy and Link kiss at the conclusion of the song.
Post-show, an argument breaks out between Corny, Velma and Mr. Spitzer, who represents the show's sponsor, Ultra Clutch hairspray. Spitzer objects to the casting of Tracy, whom he describes as "that chubby communist". Corny informs them that he plans to introduce lots of changes to the show, so that the kids in the cast will more accurately reflect the kids in the audience. Corny threatens to take the show to another network if Velma interferes. After he departs, a seething Velma decides to ruin Tracy ("Velma's Revenge").
At the Turnblad apartment, Edna fields calls from Tracy's burgeoning fan base. When Tracy gets a call inviting her to become the spokesperson for plus-size clothing outfitter Mr. Pinky, she asks Edna to represent her as her agent. Edna protests that she hasn't even left the apartment in years, but Tracy insists and Edna receives an elaborate makeover ("Welcome to the 60s").
Tracy's popularity is skyrocketing at school. Amber spreads mean-spirited rumors about her. The students assemble in gym class for a game of dodgeball. Penny and Seaweed meet and immediately hit it off. A violent game of dodgeball ensues, ending with Amber snapping the ball into Tracy's head, knocking her cold. Link reprimands Amber and goes to Tracy's aid. Tracy introduces Link to Seaweed and Penny. Seaweed invites them all to a party at his mom's record shop. When Link expresses concern that white people may not be welcome in Seaweed's neighborhood, Seaweed reassures him ("Run and Tell That").
Seaweed's song carries them into Motormouth Maybelle's Record Shop, where Seaweed introduces them to his sister, Little Inez, a dancer who was rejected at the Corny Collins auditions for being black. Motormouth Maybelle makes a grand entrance. Amber, having followed Link to the record shop, enters and is horrified at the proceedings. Velma, having followed Amber, enters immediately afterwards and is similarly horrified. Edna and Wilbur, having also been in the neighborhood, arrive as well and Velma and Edna immediately dislike each other. Velma and Amber storm out; Link refuses to leave with them. Tracy hatches a plan to integrate dancing on the TV show. Motormouth is enthusiastic but Link is reluctant to participate and departs. Edna is reluctant to participate as well, solely because she is embarrassed to be seen on TV due to her weight, but Motormouth assures her that she has nothing to be ashamed of ("Big, Blonde and Beautiful").
The protest at the studio is disrupted by the police (called by Velma). Link expresses his support for Tracy as most of those present are arrested.
The entire female cast, with the exception of Prudy, are in jail ("The Big Dollhouse"). Due to Velma's political connections, Velma and Amber are soon released. Wilbur mortgages his store to post bail for the others. However, again due to Velma's manipulations, Tracy remains incarcerated alone ("Baltimore - Reprise").
Wilbur and Edna return home, only to find that Mr. Pinky has fired Tracy as his spokesperson due to the scandal. Edna sadly recalls her own unrealized dream to design a line of queen-sized dress patterns. However, even in this time of despair and crisis, Wilbur and Edna are comforted by their shared love ("You're Timeless to Me").
Link sneaks into the jail to find Tracy. He gives her his Council ring, explaining that he took it back from Amber to give it to Tracy ("Without Love"). Meanwhile, Seaweed rescues Penny, who has been tied to her bed by her mother as punishment for going to jail without permission.
They declare their love for each other. Simultaneously, Link helps Tracy escape from jail.
Seaweed and Penny take refuge at Motormouth Maybelle's Record Shop, where Link and Tracy soon join them. By now, news of Tracy's escape from prison is being broadcast on TV. The friends are tempted to abandon their goal of integrating The Corny Collins Show, but Motormouth convinces them to struggle on ("I Know Where I've Been").
It's now the day of the live primetime spectacular broadcast of The Corny Collins Show ("It's Hairspray!"). During a commercial break, a disguised Wilbur wheels a giant hairspray can onto the set. Velma penetrates his disguise, but Seaweed and Motormouth have replaced the security guards. They pretend to eject Wilbur at her behest. Despite Tracy's fugitive status, Corny reports that she and Amber are currently neck-and-neck in the voting for Miss Teenage Hairspray. Amber performs an unflattering dance dedicated to Tracy ("Cooties"). Just as Amber seizes the crown, Tracy storms onto the set, accompanied by Link, Penny, Seaweed, Little Inez, and company ("You Can't Stop the Beat - Part 1"). Penny has been re-styled and given a cool new look. The voting now shows Tracy as the undisputed winner, and Corny crowns her Miss Teenage Hairspray 1962. Tracy declares the show officially integrated. Spitzer arrives and announces that the audience is thrilled with the show, the governor has pardoned Tracy, and he wants Velma to serve as vice president of a new line of hair products for women of color. Wilbur opens the giant hairspray can to reveal Edna dressed in finery ("You Can't Stop the Beat - Part 2"). The company celebrates a brand new day for Baltimore.