Madame Pernelle, visiting her son Orgon's house, uses the opportunity to criticize all the members of the house and to praise their boarder, Tartuffe, because he is a man of such holiness and zeal. The others present offer objections to Tartuffe, maintaining that he is false and hypocritical, but Madame Pernelle will not entertain such thoughts. As she leaves, she admonishes everyone to follow Tartuffe's precepts.
After Madame Pernelle's departure, Cléante and Dorine talk about Tartuffe and both agree that he has beguiled Orgon. Damis, Orgon's son, wonders whether his father will still allow Mariane to marry Valère; Damis must know Orgon's feelings because he wants to marry Valère's sister. He asks Cléante to question Orgon about his promise to allow the marriage to take place.
Orgon arrives and seems much more concerned about the welfare of Tartuffe than he is about his wife's illness. Cléante tries to discuss Tartuffe with Orgon, but fails and discovers that Orgon is only interested in singing Tartuffe's praises. When Orgon is questioned about the intended wedding, he dodges the issues and refuses to give a direct answer. When his daughter arrives, Orgon tells her that he wants to ally Tartuffe with his house; this he can best do by Mariane's marrying Tartuffe. Mariane is so shocked that she cannot believe her ears.
After Orgon departs, Dorine, the maid, reprimands Mariane for not having refused to marry Tartuffe. Mariane's beloved, Valère, arrives and accuses her of consenting to the marriage. Dorine listens to them argue and then, after they are reconciled, she promises to help them expose Tartuffe's hypocrisy.
Damis, incensed about Tartuffe, is also determined to reveal Tartuffe's hypocrisy, and, as he hears Tartuffe's approach, he hides in the closet. Elmire, Orgon's wife, arrives and Tartuffe, thinking that they are alone, makes some professions of love to Elmire and suggests that they become lovers. Having heard Tartuffe make such a proposition, Damis reveals himself and threatens to expose Tartuffe. When Orgon arrives, Damis tries to inform his father about Tartuffe's proposition, but Orgon is so blind that he thinks his own son is evil in trying to defame Tartuffe's good name and he immediately disinherits his son. Alone with Tartuffe, Orgon reveals that he plans to make Tartuffe his sole heir and also his son-in-law. They leave to execute this plan.
Cléante later confronts Tartuffe and tries to reason with him, but Tartuffe will only respond in religious clichés, and as soon as the opportunity presents itself, he hastily excuses himself from the room. Orgon and Elmire arrive, and when she hears Orgon's plans, she extracts a promise from him to hide in some concealed place and observe Tartuffe's actions. Orgon consents and Elmire sends for Tartuffe. When he arrives, he is accosted by Elmire, and soon he begins to make not only his declarations of love to Elmire but also derogatory comments about Orgon.
Finally convinced of Tartuffe's hypocrisy, Orgon emerges and orders him from the household. Tartuffe then reveals that legally he is now the owner of the house, since Orgon has signed over all his property. Alone with his wife, Orgon reveals that he is frightened because, earlier, he had entrusted some secret documents to Tartuffe's care — documents which could ruin Orgon's trusted position in the court.
When Orgon's mother arrives, he cannot convince her that Tartuffe is a hypocrite; it is only when news arrives that Tartuffe is having the entire family evicted that Madame Pernelle is convinced. Tartuffe brings with him officers of the court, but, as the family is about to be evicted, the officer reveals that the king has seen through the hypocrisy of Tartuffe and has ordered him to be imprisoned for this and for other crimes. The king has also restored to Orgon all of his rightful property.