The scene opens on a village on the bank of the Rhine flanked by forests and a humble-looking house on the left side, where the young and beautiful Giselle lives with her widowed mother. Across from their dwelling stands the hunting lodge of the count and his family.
Returning from his hunting trip, the forester Hilarion arrives to visit Giselle, to whom he is betrothed. But since the shutters are still closed, he leaves only a sign of his visit, hanging two freshly taken pheasants on the door.
No sooner has Hilarion departed than Count Albrecht appears in his fine clothes. He looks around and, hoping that no one sees him, dons peasant dress in the hunting lodge. He knocks on Giselle's door, hiding when the girl looks outside.
The girl spies a daisy and – despite her blind faith in the first love of her life – plucks off one petal after another, asking “He loves me? He loves me not?” The daisy seems to say “no”. Albrecht, however, employs a slight ruse in order to continue the petal-tearing, which now results in a “He loves me.” This puts both of them in a cheerful mood. Just as they are about to lose themselves in their happiness, Hilarion resolutely appears before them and jealously asks Giselle to return his affection, but is rebuffed. Albrecht's commanding intervention puts an end to the forester's advances.
Suddenly, the stage fills will young girls heading off for the harvest, who launch into a merry dance. Giselle and Albrecht are also drawn into the fun, but the weak-hearted Giselle grows exhausted and starts to stagger. Her mother comes and assures everyone that the trouble is not serious. Nevertheless, she accompanies the girl into the house.
At the sound of hunting horns, Albrecht is awakened from his daydreaming and rushes off into the forest in fright. Hilarion sneaks back, forces open the window to the hunting cabin and, with one quick motion, pulls out Albrecht's ornamental sword, and then conceals it before running off to hide himself.
The Duke of Courland and his daughter, Bathilde – Albrecht's betrothed – arrive with their hunting party for a short rest. Giselle's mother is glad to see them and, setting the table, introduces her bustling daughter to the visitors. The charming little Giselle immediately wins the favour of Bathilde, who inquires confidentially whether her new friend already has a future husband picked. After Giselle's affirmative reply, Bathilde displays her ring and reveals that she does too. Wishing Giselle all the best, the young noblewoman presents the grateful peasant girl with her necklace as a gift. The mother invites her guests into the house for refreshment.
Giselle remains out in front of the house and greets the returning harvesters, who are merrily celebrating a couple's engagement. They draw Giselle and the soon-to-be-married pair into their revelry (this is Giselle's solo variation and the so-called Peasant pas de deux).
Also returning is Albrecht, who joins the crowd of youths and is just starting to dance with his beloved when Hilarion bursts on the scene: by displaying Albrecht's sword, he proves to the company that it is no common peasant boy standing before them, but the count, who has deceived “his” Giselle. He blows a hunting horn hanging on the wall to summon the entire noble hunting party as witnesses. Bathilde gazes at her disguised fiancé in puzzlement. With a single gesture, she asks, “What is the meaning of this dress?” Smiling in confusion, Albrecht points to his own head, like someone who has just been seized by a mad idea.
Gisella is neither able nor willing to grasp what has taken place. She rushes to Bathilde to tell her that Albrecht is her love. The young noblewoman, however, informs Giselle that she is mistaken, for the count standing there before them is her own fiancé. The alarmed Giselle rips from her neck the necklace that she received as a gift and throws it down in front of Bathilde's feet. Confused and staring off into space, she starts to dance the same way she was dancing earlier with Albrecht. The prophecy of the flower petals looms in her memory. Losing her mind, her hair flying wildly, she dances incessantly. To everyone's horror, she then suddenly grabs Albrecht's sword and attempts to stab herself in the heart, but is stopped by Hilarion. Giselle then casts herself into her mother's arms and, with her final ounce of strength, turns toward Albrecht and collapses dead. Seized with remorse for his sin and standing over Giselle's corpse, the count swears eternal fidelity to the girl. Hilarion, too, is overcome by profound grief.
With head bowed in the late-night darkness and an anguished conscience, Hilarion approaches Giselle's fresh grave. He does not even realise that it is going on midnight. Mysterious, ghostly lights start to flash everywhere. The forester flees in alarm, well aware that he could easily end up in the hands of the Wilis. The Wilis – the spectres of abandoned brides – rise from their graves at midnight and take their vengeance on any men who wander their way before dawn. By pointing the myrtle branch in her hand in different directions, Myrtha, the queen of the Wilis, commands the white-clad Wilis to emerge from their graves. Then she calls forth Giselle, the newest Wili. Dressed all in white, the phantom girl rises from her grave, and the Wilis accept her as one of their own.
Another earthly being approaches – and the Wilis recoil.
Wrapped in a cloak and broken with sorrow, Albrecht arrives at Giselle's grave. Kneeling down, he covers the fresh earth with freshly picked lilies. Suddenly, he is seized by a strange feeling, as if Giselle's shade were fluttering around. He thinks he sees his departed beloved, almost as if she were alive. He follows her, but cannot catch up with her, nor touch her when he reaches for her.
The Wilis appear with Hilarion, whom they have found and overcome. Now they avenge Giselle's fate, driving the forester into a dizzying dance until he collapses dead. They then cast judgement over Albrecht, for whom a similar fate awaits. The count begs Myrtha for mercy, but in vain. Here in the realm of death, there is no pity. Giselle, however, defies Myrtha, pleading with her and shielding the young man until the queen's myrtle branch snaps in two, making it useless for issuing commands. With the break of dawn, the Wilis' power vanishes. The power of love from beyond the grave has triumphed.
As night turns to day, the stunned Albrecht is not sure whether he is awake or dreaming. Did he really experience the ghostly night? Did he actually meet his beloved? The proof emerges when Giselle appears before him one more time. Clutching his dropped flower close to him, Albrecht staggers hesitantly out of the gloom of the tree-ringed cemetery.