The play takes place at Mr. Jourdain's house in Paris. Jourdain is a middle-aged "bourgeois" whose father grew rich as a cloth merchant. The foolish Jourdain now has one aim in life, which is to rise above this middle-class background and be accepted as an aristocrat. To this end, he orders splendid new clothes and is very happy when the tailor's boy mockingly addresses him as "my Lord". He applies himself to learning the gentlemanly arts of fencing, dancing, music, and philosophy, despite his age; in doing so he continually manages to make a fool of himself, to the disgust of his hired teachers. His philosophy lesson becomes a basic lesson on language in which he is surprised and delighted to learn that he has been speaking prose all his life without knowing it.

Par ma foi ! il y a plus de quarante ans que je dis de la prose sans que j'en susse rien, et je vous suis le plus obligé du monde de m'avoir appris cela.

My faith! For more than forty years I have been speaking prose while knowing nothing of it, and I am the most obliged person in the world to you for telling me so.

Madame Jourdain, his intelligent wife, sees that he is making a fool of himself and urges him to return to his previous middle-class life, and to forget all he has learned. A cash-strapped nobleman called Dorante has attached himself to M. Jourdain. He secretly despises Jourdain but flatters his aristocratic dreams. For example, by telling Jourdain that he mentioned his name to the King at Versailles, he can get Jourdain to pay his debts. Jourdain's dreams of being upper-class go higher and higher. He dreams of marrying a Marchioness, Dorimène, and having his daughter Lucille marry a nobleman. But Lucille is in love with the middle-class Cléonte. Of course, M. Jourdain refuses his permission for Lucille to marry Cléonte.

Then Cléonte, with the assistance of his valet Covielle and Mme Jourdain, disguises himself and presents himself to Jourdain as the son of the Sultan of Turkey. Jourdain is taken in and is very pleased to have his daughter marry foreign royalty. He is even more delighted when the "Turkish prince" informs him that, as father of the bride, he too will be officially ennobled at a special ceremony. The play ends with this ridiculous ceremony, including Sabir standing in for Turkish.