Act 1

The show opens as the citizens of Oz rejoice over the death of the Wicked Witch of the West. Glinda descends onto the stage and confirms the circumstances of the Witch's melting, and explains how the Witch was the result of a relationship her mother had with a stranger, and her father hated her for being green ("No One Mourns the Wicked"). The remainder of the plot forms an extended flashback through the events of Glinda's and the Witch's lives.

It starts at Shiz University ("Dear Old Shiz") when Glinda, then Galinda Upland, and Elphaba, along with her disabled sister Nessarose, start school together. Elphaba's father instructs her to take care of Nessarose, his favorite, and presents his handicapped daughter with a beautiful pair of jeweled shoes. Madame Morrible, the Headmistress of Shiz University, introduces herself to the students and puts Galinda and Elphaba in a room together, much to their chagrin. However, once Morrible notices Elphaba's innate magical talent, she declares that Elphaba could be the right-hand to the Wonderful Wizard of Oz someday, and Elphaba daydreams about what she and the wizard could accomplish together (“The Wizard and I”). Galinda and Elphaba then write home and reflect on their unfortunate roommate assignment (“What is this Feeling?”).

The audience is introduced to Dr. Dillamond, a Goat and Shiz University's only Animal professor, whose history class is interrupted by an anti-Animal demonstration. After dismissing the class, he confides in Elphaba that things in Oz are not what they seem to be; something is causing the Animals of Oz to lose their powers of speech ("Something Bad").

Fiyero Tiggelar, a Winkie prince, arrives at Shiz and immediately impresses his own brand of cavalier, carefree living on the students ("Dancing Through Life"). He organizes a party at a local ballroom. A munchkin named Boq tries to ask Galinda to the ball, but Galinda, who wants Fiyero as her date, distracts him by telling him to invite Nessarose. Later, Galinda, while preparing, discovers a black pointed hat in a box and gives it to Elphaba as a “present"; Elphaba arrives wearing the hat, only to be ridiculed. Defiant, she proceeds to dance alone and without musical accompaniment. Madame Morrible shows up and presents Galinda with a training wand from Elphaba, who is grateful for Galinda's "kindness" towards her and Nessarose. Feeling guilty, Galinda joins Elphaba on the dance floor, marking the start of a new friendship between the two. After the dance, Galinda and Elphaba talk in their room; Galinda decides to give her new friend a makeover and to make her "Popular." Elphaba confesses that her father hates her because what happened to Nessarose is her fault; her mother ate too much of a special plant to prevent her next baby from being green. Nessarose's legs were permanently damaged, and her mother died giving birth to her. Galinda reveals that she's going to marry Fiyero; he just doesn't know it yet.

The next day, Ozian officials take away Doctor Dillamond. The new history teacher arrives with a caged lion cub as the subject of an in-class experiment, revealing that animals that are kept in cages never will learn how to speak. Outraged, Elphaba and Fiyero steal the cub and set it free. The two realize that they may have feelings for each other, but Fiyero leaves, embarrassed. Elphaba takes refuge under a bridge and states that it would be impossible for someone like Fiyero to love someone like her ("I'm Not That Girl"). Madame Morrible finds her and announces that she has been granted an audience with the Wizard. At the train station, Galinda and Fiyero see Elphaba off to the Emerald City. In an attempt to impress Fiyero, Galinda announces that she will change her name to "Glinda" in honor of Doctor Dillamond's persistent mispronunciation. Fiyero seems not to notice, focusing his attention instead on Elphaba, and feeling bad for Glinda, Elphaba invites her along to see the Wizard.

After a day of sightseeing in the Emerald City ("One Short Day"), Elphaba and Glinda meet the Wizard. Eschewing the special effects that he employs for the benefit of most visitors, he invites Elphaba to join him ("A Sentimental Man"). He tells Elphaba that Madame Morrible has told him all about her particularly strong abilities in sorcery, and reiterates that this is why he has invited her; simultaneously, out of the shadows, Madame Morrible herself suddenly appears, explaining that she had followed Elphaba to ensure that she was well-received, and that she now works alongside the Wizard as Press Secretary of the Land of Oz.

Elphaba is very surprised to see Madame Morrible but does not express offence at having been followed, and congratulates her on her 'promotion'. It very quickly becomes apparent that Madame Morrible and the Wizard, far from being strangers as viewers had earlier been left to assume, in fact have a close personal friendship, and are in league together in a peculiarly unsettling way, the cause of which is not yet revealed.

As a test of her abilities, which the Wizard assures Elphaba he is already confident in, he asks that Elphaba give his monkey servant, Chistery, the ability to fly using the Grimmerie, an ancient book of spells. Elphaba demonstrates an innate understanding of the lost language, and successfully gives Chistery wings. It is then that the mood of this scene turns decidedly darker, for the Wizard, in prompting her to cast this spell, had not merely done so to give his single monkey servant wings. Showing her how powerful she really is, the Wizard excitedly reveals an enormous cage full of winged monkeys, and remarks that they will make good spies to report any subversive Animal activity. Madame Morrible is just as excited and exuberant, remarking that she had known that Elphaba could do this all along.

But Elphaba is horrified. She recognizes that it is in fact Madame Morrible and the Wizard who are behind the political and social oppression of the Animals, and not extremists, as had been claimed by various people in Shiz before. It is also implicitly recognized that Madame Morrible, while publicly expressing what appeared to be deep regret over the firings and exiles of various Animal faculty members at Shiz University, had actually been the source of those very firings and exclusions the whole time.

All of these connections gather rapidly in Elphaba's consciousness within a matter of a few seconds ....and as they do, and her angry accusations towards both Morrible and the Wizard gather force, these two Oz Government administrators cease to hope that Elphaba will join them, and decide to regard her as an enemy subversive. Elphaba is more incredulous than angry at this point, hurt she has been used and that the Wizard has no power of his own, meaning that she cannot believe in him as a great man the way she had been doing all those years at school. Elphaba and Glinda both run away from the situation as fast as they can, the Grimmerie still in Elphaba's hands, pursued by the palace guards.

Elphaba and Glinda run into the tallest tower, where they hear Madame Morrible declaring to all of Oz that Elphaba is a "Wicked Witch" and is to be distrusted. Elphaba enchants a broomstick to fly, and tries to convince Glinda to join her in her cause, but Glinda cannot resist the call of popularity, and refuses. At that point, the Guards break down the tower door, rushing in and grabbing Glinda, assuming she is in league as a 'subversive'.

But Elphaba, wielding the broomstick menacingly at the guards and screaming that Glinda "had nothing to do with it", at first knocks them back forcefully with an invisible repellent energy blast, and then levitates, defiantly singing down at the guards, and then at a crowd of angry Oz citizens, about how she plans to fight the Wizard with all of her power ("Defying Gravity"). Act 1 ends with Elphaba raising her broom in a revolutionary-style salute, after which the stage goes black.