The film focuses on several months of Molière's early life that are unknown to scholars. It begins in 1658, when the French actor and playwright returns to Paris with his theatrical troupe to perform in the theater the king has given him. Most of the film is in the form of a flashback to 1645. Following an unsuccessful run as a tragic actor, Molière is released from debtor's prison by Monsieur Jourdain (Fabrice Luchini), a wealthy commoner with social pretensions, who agrees to pay the young actor's debts if Molière teaches him to act. Jourdain, already a married man with two daughters, hopes to use this talent to ingratiate himself with Célimène (Ludivine Sagnier), a recently widowed beauty and wit with whom he has become obsessed, by performing a short play he has written for the occasion. Molière, however, who has been presented to the family and staff of Monsieur Jourdain as Tartuffe, a priest who is supposedly to serve as tutor for the Jourdains' younger daughter, proceeds to fall in love with Jourdain's neglected wife, Elmire (Laura Morante). Sub-plots involve the love life of the Jourdains' older daughter, and the intrigues of the penniless and cynical aristocrat Dorante (Edouard Baer) at the expense of the gullible Jourdain.
The story is mostly fictional, in the manner of Shakespeare in Love. Many scenes and text in the script follow actual scenes and text in Molière's plays (including Tartuffe, Le Misanthrope, and Le Bourgeois Gentilhomme, whose principal character is also named Jourdain), in a manner that implies that these "actual" events in his life inspired the plays of his maturity. This is a recurrent plot device in the film, since Célimène is the main character's love interest in The Misanthrope.