The overjoyed girls of UCLA's sorority Delta Nu, led by Margot, Serena, and Pilar, celebrate the engagement of Warner Huntington III to their perky, sweet, and strikingly blonde sorority president, Elle Woods, who is fretting over finding the perfect dress for the occasion ("Omigod You Guys"). Once she acquires her dream dress, Elle goes to dinner with Warner, where he tells her that he needs someone more serious ("Serious") and breaks up with her. Elle is devastated and sulks for twelve days but decides to chase Warner to Harvard Law School to show him that she can be serious. With help from Delta Nu sister Kate, Elle studies for the LSATs. Instead of writing a personal essay, Elle bursts into the Harvard admission offices backed by a squad of cheerleaders. She is accepted after revealing she is motivated by love ("What You Want").
Elle's snobby classmates disapprove of her attire, and the only person who is willing to help her is law teaching assistant, Emmett Forrest ("The Harvard Variations"). However, he cannot protect her in class from the blood-thirsty Professor Callahan ("Blood in the Water"). Callahan kicks the under-prepared Elle out of class at the suggestion of her classmate Vivienne Kensington, who happens to be Warner's new girlfriend. This "tragedy" summons the apparitions of the sisters of Delta Nu, who, acting as a Greek Chorus visible and audible only to Elle, tell her to stay positive ("Positive"). Elle, deciding that being blonde is the problem, decides to become a brunette. She heads to the Hair Affair salon where she meets the spunky beautician Paulette, who tells Elle that when she is down, she puts on her favorite CD, and dreams of Ireland ("Ireland"). At the salon, Vivienne gives Elle an unexpected invitation to a costume party. Paulette sends Elle off with a costume for the party, her positivity and blonde hair still intact ("Ireland (Reprise)").
Walking into the party as a Playboy Bunny, Elle soon realizes that she was tricked by Vivienne but courageously seeks Warner in an effort to win him back, leaving him unimpressed ("Serious (Reprise)"). Elle runs from the party, only to meet Emmett, who struggles to understand Elle's love problems. He has Elle assess her priorities until she realizes it is her obsession with Warner that keeps her from earning his respect ("Chip on My Shoulder"). Freed from her need to please Warner, she defeats him in a classroom debate. Elle then helps Paulette in a way that proves she is beginning to understand law. Warner and Vivienne win two of Callahan's coveted internship positions, and Warner proposes to Vivienne on the spot right in front of Elle. Vivienne accepts, with a kiss and a yes. Before Elle's heart can break, Emmett shows her the internship list. Below the names of Vivienne, Warner, and classmate Enid Hoopes is the name Elle Woods, at which she is ecstatic ("So Much Better").
Act II begins with fitness queen, Brooke Wyndham, and her fitness team's workout video, which is being viewed by Elle, Callahan, Emmett, Vivienne, Warner, and Enid ("Whipped Into Shape"). Callahan tells the legal team that Brooke is accused of murdering her billionaire husband. The "video" then turns into a scene from the jail, where Brooke leads the inmates into a fitness frenzy. Brooke then privately tells Elle her alibi, that she was getting liposuction, but makes Elle promise not to tell anyone ("Delta Nu Nu Nu"). Because of Elle's loyalty to her client and refusal to state the alibi, Elle and Emmett are shunned by the group. To cheer Emmett up and to increase his chances of impressing Callahan, Elle gives him a makeover ("Take It Like A Man").
Back at the Hair Affair, Elle is getting a manicure when Kyle, the sexy UPS guy, walks into the salon to deliver a package to Paulette. Paulette is in complete awe. When he leaves, Pilar, Serena, and Margot are summoned by Paulette's amazing "Bend and Snap" when picking up the UPS package. The sorority girls tell Paulette to use the "Bend and Snap" on Kyle, but when she does, she accidentally breaks his nose ("Bend and Snap").
In the courtroom, we see Nikos, Brooke's pool boy, being questioned by the D.A. about his "love affair" with Brooke. After doing the Bend and Snap in front of Nikos and getting no attention, Elle is convinced that Nikos is gay. Callahan and her teammates do not believe her, simply thinking that he is just European ("Gay or European!"). Emmett decides to question Nikos on the stand, and successfully makes Nikos slip and state his boyfriend's name Carlos. Niko quickly covers that he misunderstood the word "boyfriend" as "Best Friend." Carlos, Niko's Boyfriend, appears at the end of the courtroom, fed up with the closeted nature of his boyfriend, and proclaims Nikos's homosexuality. At the end of the song, Nikos confesses that he is indeed gay AND European.
Later that night in Callahan's office, the interns celebrate Elle's skill. Warner finds problems with calling a finely tuned awareness of homosexuality a legal victory. Callahan, annoyed with Warner's behavior, sends Warner out of the room to fetch a coffee. Callahan dismisses Emmett and the other interns but requests Elle to remain for a few moments. Callahan forcibly kisses Elle, who slaps him. In turn, Callahan fires her. Warner and Vivienne both saw the kiss through the door of the room. Warner turns away in anger, leaving Vivienne to be the only one to witness the slap. After Callahan leaves, Warner re-enters the office and mocks Elle, but Vivienne tells him to shut up and they both leave. A defeated Elle prepares to go home, even though Emmett asks her to stay, finally realizing that he is in love with her ("Legally Blonde").
Elle heads to the Hair Affair to say goodbye to Paulette, but before she can leave, Vivienne and Enid convince Elle otherwise ("Legally Blonde Remix"). Elle discards her lawyerly navy suits, dons a pink dress (or pink lawyer suit) and leads a parade back to the courtroom. They meet Kyle on the way, who takes a liking to Paulette, and reveals himself to be the Irish man of her dreams, prompting to Irish Dance amongst the ensemble. Back at the trial, Brooke fires Callahan and hires Elle. Brooke's stepdaughter Chutney goes to the witness stand and her testimony is damning, stating after she got out of the shower she saw Brook covered in her father's blood. After Chutney states she received a perm the day of the murder, Elle realizes a flaw in Chutney's alibi and suggests that the entire court should be moved to the scene of the crime - the bathroom where the murder took place ("Scene of the Crime"). As a demonstration, Elle asks Paulette to give Enid a perm, and asks Enid to step into the shower upon entering the crime scene. Relying on her knowledge of hair maintenance, Elle's demonstration is successful as Enid walks out of the shower with completely flattened hair—revealing that Chutney could not have possibly gotten a perm because her hair was still intact. Under Elle's intense questioning, Chutney accidentally confesses that she killed her father. Warner proposes to Elle, having been dumped by Vivienne. Elle gently refuses, claiming to have been changed by the experience ("Find My Way").
Three years later, Elle ends up as the valedictorian of her class. Paulette tells the audience that Elle is not one to brag about her valedictorian status, so she decided to allow Paulette to play "Where are they now" during her speech. Paulette says that Enid practices family law, Vivienne is training for the Peace Corps, and Warner dropped out and pursues a modeling career. Callahan ran for governor but was defeated, and his wife hired Emmett to handle their divorce. Paulette married Kyle, had two kids, and is pregnant with a third. They live in Worcester, Massachusetts and Paulette bought a new salon (the Worcester detail was taken from the London script, and replaced with the detail that a child of hers was named Seamus) At the end of the graduation, Elle proposes to Emmett, and Emmett accepts ("Finale").