It's early June, 1962, in blue-collar Baltimore. Surrounded by "45s" and teen magazines, Tracy Turnblad wakes up in her family's apartment over the Har-De-Har Hut, her father, Wilbur's jokeshop (GOOD MORNING BALTIMORE). Teenager Tracy is a large girl with a high hairdo, abundant joie de vivre and rhythm in every inch of her body. Her obsession is the Corny Collins TV show on WZZ1, the after-school dance program that has made stars out of THE NICEST KIDS IN TOWN. Everyday, Tracy and her shy best friend, Penny, rush to Tracy's house right after school to learn the latest dances and moon over Link Larkin, the show's resident dreamboat. Tracy's mother, Edna, a hardworking woman of vast proportions and enormous heart, takes in laundry to make ends meet. Penny's mother, Prudy Pingleton, disapproves of the "coloured" music, but to Edna, it's just good old black-and-white TV.

On the Corny Collins Show, the reigning queen is the oh-so-perfect Amber Von Tussle, whose overbearing mother, Velma, happens to be producing the show. They are all excited about a coming nationwide prime-time event, Corny Collins Spectacular: Live from the Eventorium, sponsored by Ultra Clutch Hairspray. The girl on the show who gets the highest popularity rating will be crowned Miss Teenage Hairspray, and Amber wants that crown almost as much as Velma wants it for her. The daily show is segregated except for once a month, when Motormouth Maybelle co-hosts "Negro Day." Velma complains that Corny spinning so much "race" music will lose them their sponsor, while Link asks Amber to go steady and gives her his Corny Collins Council ring. One of the girls on the show will be dropping out for a suspicious nine months, and auditions are announced for a replacement. Tracy and Penny are dying to go. Edna, Prudy and Velma each try to control their daughters, but the girls rebel (MAMA, I'M A BIG GIRL NOW).

Tracy and Penny are late for the audition, due to a "stupid bus crash", but when Link bumps into Tracy, she hears a symphony (I CAN HEAR THE BELLS). The girls on the Council, led by Amber, pick Tracy apart, and Velma won't even let her dance (THE LEGEND OF MISS BALTIMORE CRABS). Back in school and in detention again for outlandish hair-do, Tracy meets all the cool black kids in school, especially Seaweed, who teaches Tracy some fabulous moves that she uses at the Sophomore hop. DJ Corny Collins singles her out, and so does Link. All they had to do was see her dance. Next time we see her, she's on the show. Over Amber's objections, Link sings Tracy a love-song on the air on which Tracy brazenly joins in and they end it with a kiss (IT TAKES TWO). Not only does Tracy eclipse Amber, she also suggests that every day be "Negro Day" right on the air, much to Velma's fury.

Tracy gets home to Edna, and the offers are pouring in. Mr. Pinky from The Hefty Hideaway wants her for his spokesgirl and "fashion effigy." Tracy wants Edna as her agent, but Edna is reluctant to leave the house. Tracy insists she get with the decade. Thanks to Mr. Pinky, the Turnblads are transformed from frumps to fashion-icons, extra-large deluxe (WELCOME TO THE '60s).

At school, Tracy is attacked by Amber in a game of dodgeball but Penny, Link and Seaweed come to her aid. Seaweed invites them all to a platter party at the record shop run by his mother, Motormouth Maybelle, in the black section of town. Tracy thinks that's so cool, but Seaweed says not everyone sees it that way. At Motormouth Maybelle's shop, Seaweed is joined by his sister, Li'l Inez (RUN AND TELL THAT!). Black kids and white kids are all dancing together when one by one, Amber, Velma, Edna and Wilbur arrive. Amber and Velma try to make Link leave with them, but he stays and they go. Tracy schemes with Maybelle to integrate the show, starting tomorrow on Mother-Daughter Day. Maybelle will bring Li'l Inez, with Tracy and Edna blocking the door behind them. Link chickens out, afraid that controversy will cost him his big break on the nationwide special, and he leaves. Tracy is heartbroken, but unwilling to back down. Edna feels she could never appear on camera at her current weight, but Maybelle insists that, like her, Edna is BIG, BLONDE AND BEAUTIFUL. Edna agrees, but as they reach the studio, their civil rights demonstration turns into a full-scale riot, and both protesters and protestees are loaded into a police paddy wagon.

Almost every woman in town is in jail, waiting to be sprung from THE BIG DOLLHOUSE. After Velma and Amber are pardoned, Wilbur posts bail for everyone else by mortgaging the Har-De-Har Hut. However, thanks to some legal shenanigans by the Von Tussles to keep her out of the Miss Teenage Hairspray contest, Tracy is moved to solitary "refinement" (GOOD MORNING BALTIMORE - REPRISE). Back at home, Wilbur is working on a giant joke can of hairspray, while Edna bewails Tracy's fate as well as her own forgotten dreams of being a fabulous fashion designer. Even Mr. Pinky wants all his glamorous outfits back. She's feeling old and worn-out. But Wilbur knows just what to say (TIMELESS TO ME).

Link slips into jail past a sleeping guard to whisper to Tracy through the bars of her cell that he's through with Amber, who was just using him to look popular. He wants Tracy to be his girl and wear his Corny Collins Council ring. Meanwhile, Prudy's mother has tied Penny up in her room, but Seaweed comes to set her free. Link cuts through the bars of Tracy's cell with a blowtorch made from a can of hairspray and a Zippo lighter (WITHOUT LOVE).

They run to Motormouth Maybelle's, where they plan their next move - the integration of the Miss Hairspray contest. Tracy is afraid of what it will cost her friends and family, but for Motormouth, it's too late to turn back (I KNOW WHERE I'VE BEEN). At the Baltimore Eventorium, armed guards surround the Miss Teenage Hairspray spectacular, as Corny and The Council Members sing their big opening number, HAIRSPRAY. A scoreboard of votes for Miss Hairspray shows Amber and Tracy are neck-and-neck. A man wheels on a giant can of hairspray, but Velma recognises him as Wilbur and thinking this Trojan Horse houses his jailbird daughter, calls the riot police away from the entrance to guard it.

It's time for the contestants' new dance competition. Amber dedicates her number, COOTIES, to Tracy "the Loser". Amber is claiming the prize as Tracy bursts in, followed by Link, Penny and Li'l Inez. The armed guards turn out to be Seaweed, Motormouth and the kids from the other side of the tracks. Finally entering through the front door, everybody joins in Tracy's dance and The Corny Collins Show is officially integrated, live and nationwide. The giant can of hairspray explodes to reveal Edna making her coast-to-coast television debut in a fabulous ensemble of her own creation. The dancing crowd then turns on Velma and Amber, inviting even them to admit YOU CAN'T STOP THE BEAT.