Baltimore, 1962, the civil rights movement is in full swing and times are changing. Tracy Turnblad ( Nikki Blonsky) is an ordinary teenager who loves to dance [Good Morning Baltimore]. Tracy and her best friend Penny Pingleton ( Amanda Bynes) rush home from school each day to watch the Corny Collins Show (CCS), a hip dance show for teenagers [Nicest Kids in Town].
One day the show announces that they are going to hold open auditions for a new council member (teen dancer) to replace one that is leaving. Penny encourages Tracy to audition much to the disapproval of Tracy's mum, Edna ( John Travolta) and Penny's mum, Prudy ( Allison Janney). Her father, Wilbur ( Christopher Walken), is more supportive and tells her to go for it.
At the audition, although being a great dancer, Tracy is rejected by the shows producer, Velma Von Tussle ( Michelle Pfeiffer), for being overweight and pro-racial integration [(The Legend of) Miss Baltimore Crabs]. Things get worse for Tracy at school where she is sent to detention for skipping school. Much to her surprise, detention is full of kids who take part in the CSS's 'Negro Day' and they use there time in detention to show off their dance moves. Seaweed ( Elijah Kelley), the son of 'Negro Day' presenter Motormouth Maybelle ( Queen Latifah), shows her some new dance moves and cathches the eye of Penny. Tracy's then leaves detention and accidentally crashes into Link Larkin ( Zac Efron), teen heartthrob and lead male dancer on the CCS, and begins to hallucinate of a life they might have together [I can Hear the Bells].
Later, at an open dance attended by the CCS council, Tracy shows off her moves and grabs the attention of Corny Collins ( James Marsden) himself [Lady's Night], who immediately invites her to join the council [Nicest Kids in Town (Reprise)]. Tracy proves to be a hit and garners much popularity. This angers Amber Von Tussle ( Brittany Snow), daughter of Velma and the shows main female dancer, as her chances of being crowned 'Miss Teenage Hairspray' are threat as well as her relationship with Link [New Girl in Town]. Tracy's new-found popularity also gets an advertisement deal with Mr. Pinky ( Jerry Stiller), owner of Mr. Pinky's Hefty Hideaway. After much convincing, Tracy persuades her mother, reluctant to leave the house because of her appearance, to accompany her as her agent and ending Edna's fears of being shunned by a world that's changed much since she was a teenager [Welcome to the 60s].
After being sent to detention again, this time by Amber, Link decides to join Tracy. Seaweed asks them, along with Penny and his sister Lil' Inez ( Taylor Parks), to follow him to his mother's record shop where there is a sock hop (sponsored dance) happening [Run and Tell That]. Edna bursts in took take Tracy back home but Maybelle is able to dissuade her from doing so [Big, Blonde and Beautiful]. Maybelle then reveals the news that 'Negro Day' has been cancelled by Velma. Angered, Tracy organises a protest march for the day prior to the Miss Teenage Hairspray contest . Seeing the show as his only chance at true stardom, Link decides to not join in the march which breaks Tracy's heart.
Meanwhile, Velma concocts another plan to make sure Amber wins the contest. She goes to the Hardy-Har-Hut, owned by Wilbur, and tries to seduce him into committing infidelity [Big, Blonde and Beautiful (Reprise)]. He resists her advances but is caught in a compromising position by Edna who suspects him of having an affair. Eventually, the pair make up [(You're) Timeless to me] but not before Edna bans Tracy from going on the protest.
Defying her mother, Tracy sneaks out and joins the protest which is halted by a police blockade instigated by Velma [I Know where I've Been]. The protesters are swiftly arrested but Tracy tries to escape by hiding at Penny's. Prudy finds Tracy and has her arrested while also locking Penny away in her room.
Wilbur is able to secure the bail of all of those imprisoned except Tracy. Seaweed, along with his friends, use the initiative to break out Penny and Tracy from their respective predicaments [Without Love]. At the same time, Link goes to Tracy's house to find her and realising the true feelings he has for her.
At the show [It's Hairspray], Velma has rigged the contest making sure that Amber will be the winner. She also created a police barrier around the studio so Tracy and the others won't be able to come in. A disguised Edna and Penny quietly make there way into the competition while, simultaneously, Wilbur, Seaweed and the others help get Tracy into the building. Seeing Tracy, Link abandons Amber to dance with her. A little later, Lil' Inez and Motormouth Maybelle arrive with Link bringing Inez onto the stage to dance.
Lil' Inez goes onto win the competition after receiving the most votes and thus making the CSS fully integrated much to the dismay of Velma who, being recorded unknowingly, loudly tells of her vote fixing scheme. This gets her fired bringing about much jubilation and ending the film with Link and Tracy finally kissing [You Can't Stop the Beat].