At the Delta Nu sorority house, word is out that Elle Woods is going to dinner to get engaged to her beau, Warner Huntington III ("Omigod You Guys"). Margot, Serena and Pilar lead the other Delta Nus to the mall, where Elle is having trouble choosing the right dress for the occasion. Later at dinner, just when Elle is sure Warner is going to propose, he breaks up with her, explaining that, with his departure for Harvard Law School, it's time to get serious ("Serious"). Devastated, Elle locks herself in her room. Twelve days later, the Delta Nus finally get Elle to emerge ("Daughter of Delta Nu"). Elle realizes the only solution to her heartache is to get into Harvard Law and prove to Warner she's serious enough for him ("What You Want"). Sorority sister, Kate, helps Elle study for the LSAT and, after several attempts and a lot of hard work, Elle's application comes before Harvard Admissions. Lowell, Winthrop and Pforzheimer, three Harvard admissions coordinators, decide to admit Elle after a very extravagant song and dance (which she submits in lieu of a personal essay), citing love as her main motivation.

On the first day of class, Elle meets her fellow first-year law classmates, Aaron, Padamadan and Enid, as well as Warner, who is shocked to see her on campus. Callahan (the most feared teacher at Harvard) kicks Elle out of class for being unprepared at the suggestion of classmate, Vivienne Kensington. Callahan's TA, Emmett, tries to console Elle, but her mood only worsens when Warner confesses to Elle that Vivienne is his new girlfriend. Elle finds the nearest salon and meets Paulette, who commiserates with her situation ("Ireland").

Afterward, Elle runs into Vivienne, who invites her to a costume party. Elle attends, hoping to see Warner, but is dismayed to discover she is the only one who wore a costume – much to Vivienne's delight. On the way home, Elle meets Emmett, who tells Elle how hard he's worked to get where he is and encourages her to do the same ("Chip on My Shoulder").

Time is passing quickly at law school, and Elle is working harder than ever, eventually winning her first court case in class and receiving a recommendation to apply for Callahan's internship. With her newfound confidence, Elle helps Paulette win her dog back from her estranged boyfriend, Dewey.

Back at Harvard, Warner and Vivienne win two of Callahan's coveted internship positions, and Warner proposes to Vivienne on the spot, right in front of Elle. Before her heart can break, Emmett shows her the internship list, and Elle is ecstatic to discover her name is on it as well ("So Much Better").

The interns quickly jump into the case of fitness video guru, Brooke Wyndham, who is accused of killing her wealthy husband. After watching her fitness video ("Whipped into Shape"), the interns meet her at a correctional facility, where she refuses to give her alibi to anyone but Elle, thanks to their Delta Nu sisterhood ("Delta Nu Nu Nu"). In confidence, Brooke shares with Elle that she was getting liposuction the day her husband was killed, so there is no way she could be guilty, but no one can know because her fitness empire would be destroyed. The other interns demand that Elle give up Brooke's alibi, but Elle refuses to go against her Delta Nu pledge.

Back at the salon, Paulette has eyes for the UPS delivery man, Kyle, but isn't confident enough to go after him. Elle teaches her a guaranteed move to win any guy's affections – the Bend and Snap ("Bend and Snap"), but when Paulette tries it, she accidentally breaks Kyle's nose.

Elle returns to the case, but Callahan has a different agenda and tries to kiss her... just as Vivienne returns, unnoticed. Elle rejects Callahan's advances and is fired. Defeated, she prepares to go home, convinced she was only ever seen as a joke, even though Emmett asks her to stay, finally realizing that he is in love with her ("Legally Blonde"). Elle stops by the salon to say goodbye to Paulette, but Vivienne – who witnessed what happened to Elle in Callahan's office and finally understands her – convinces her to keep fighting. The entire salon rallies behind Elle as she heads back to the courtroom ("Legally Blonde – Remix"), where Brooke fires Callahan and hires Elle to continue her defense.

Everyone is present to witness Elle's first day in court, including Paulette and Kyle (now a couple), Margot, Serena, Pilar and the other Delta Nus. Brooke's stepdaughter, Chutney, takes the stand to testify that, when she got out of the shower, she witnessed Brooke standing over her father's body, covered in blood. When asked what she had been doing earlier that day, Chutney reveals she had gotten a perm, and Elle realizes a flaw in Chutney's alibi – she couldn't possibly have showered the same day as receiving a perm, or her hair would be flattened. Since her perm is still intact, she has obviously lied about her alibi. Under some intense questioning from Elle, Chutney accidentally reveals that she killed her father, mistaking him for Brooke. Elle wins the case, and Brooke is set free. Warner tries to propose to Elle, but she gently refuses, having gained her independence and a desire to be the best she can be ("Find My Way").

Three years later, Elle is made valedictorian of her class and, in her commencement speech, she proposes to Emmett, who accepts. Everyone celebrates their legally blonde friend and heroine, Elle Woods ("Finale").