Alceste, the misanthrope, explains to Philinte that he hates mankind because there is so much hypocrisy, deceit, and false flattery in the world that he can't find a man who will speak the truth openly. He asserts that all people should be completely frank and honest with one another. Philinte asks Alceste to be more tolerant because it is a part of human nature to flatter other people and to enjoy a certain amount of gossip. At this point, a fashionable man about town, Oronte, appears and asks Alceste to evaluate a poem he has just written. Alceste reads the poem and gives Oronte an honest answer — the poem is wretched and Oronte should give up trying to write poetry. Oronte, who has asked for an honest answer, is insulted when Alceste speaks frankly, and leaves in an indignant huff. Philinte points out to Alceste that his honesty has created an enemy, when a little innocent flattery would have won him a friend.
When Alceste meets Célimène, the woman he loves, he immediately begins to reproach her for her coquettish and flirtatious behavior. He dislikes the fact that she treats all people with the same charm and grace. She tells him that it is better to treat all people equally than for her to closet herself and heap all her favors on one person. In the midst of the argument, two fops, Acaste and Clitandre, arrive, followed by Philinte and Eliante, a woman of good reasonable sense. The fops immediately begin gossiping about various members of the court, and to Alceste's chagrin, Célimène joins in the gossip by castigating every person who is mentioned. Alceste cannot tolerate this, and tries to stop the performance. Shortly afterward, an officer arrives with a summons for Alceste. He is to appear before the court of the marshals because of his comments about Oronte's poem.
Later at Célimène's house, the two fops talk about her, but abruptly cease when she appears. Soon afterward a servant announces the arrival of Arsinoé a lady of society. When the fops leave, Arsinoé pretends to inform Célimène of the gossip being spread about her. In turn, Célimène tells Arsinoé what is being said about her. When Alceste arrives, Célimène excuses herself and leaves Arsinoé and Alceste together. Immediately, Arsinoé begins flattering Alceste and offers to show him proof that Célimène is false to him.
In the following scene Philinte reports to Eliante that Alceste would not retract what he had said about Oronte's poem. Eliante admits that she must admire a man who sticks to his opinion so firmly; in fact she would not mind having him as a suitor. Philinte then confesses his love for Eliante and his own desire for her hand if she does not become involved with Alceste. When Alceste arrives, he is in a rage against Célimène for being false. Arsinoé has given him a love letter which appears to be from Célimène to someone else. When he confronts Célimène with the proof, she simply ignores it and suggests that it might have been written to a woman and not a man. She then accuses Alceste of being too strict and of not caring for her. Before the argument is settled, Alceste is reminded of a lawsuit against him, which he is apparently about to lose and which must be tended to immediately.
Later, Alceste is complaining to Philinte about the injustice in human society: He has indeed lost his lawsuit even though his case was a just one. He decides that he will retire from mankind and live in solitude. When Célimène comes in accompanied by Oronto, both men insist that she choose one of them. She avoids making a choice and before the two men can force her, the two fops, Clitandre and Acaste, arrive with incriminating letters which Célimène has written. In these letters, she made derogatory remarks about all of the gentlemen. The fops leave, promising to publish her perfidy to all of society. Oronte also gives up his suit to Célimène. Left alone with Alceste, Célimène acknowledges her mistake and offers her hand to Alceste if he will still have her. He then tells her that he wants to retire from society and wants her to join him in solitude. But Célimène cannot forego society, and at this point Alceste is cured of his love for Célimène and dismisses her. He then promises to live alone and rail against all of society and mankind.