The play's plot generally follows that of the original story, focusing on a young 19th century Parisian girl being groomed for a career as a courtesan. Gigi lives with her mother and grandmother, and takes lessons at the home of her aunt. Her lessons include social manners, conversation, and personal relationships. The family has significant social connections, and have been great friends with the rich playboy Gaston. Gaston is bored with his life, and his only joy seems to be in the company of Gigi and her family.
Aunt Alicia decides that the time is right for Gigi's entry into society. After dressing her up, she is presented to Gaston as a young woman. He is, at first, dismayed at the change. Gradually he realizes that he is attracted to Gigi, and takes her out on the town. As the night progresses, Gaston sees the emptiness of his life and wants something more. He proposes marriage to Gigi, and she gladly accepts.