This Act contains two important scenes that are vital in terms of the plot of this excellent Shakespearian comedy. Act IV scene 1 features the long-awaited marriage of Hero to Claudio, except that instead of marrying, Claudio uses the ceremony as an opportunity to denounce Hero of being sexually promiscuous. Don Pedro and Don John supports his claim, and the three men leave together. Leonato is furious and Hero faints. The Friar believes in the innocence of Hero and persuades Leonato to announce Hero's death so that she can start a new life in hiding. Benedick comforts Beatrice and both confess their love for each other. Beatrice also forces Benedick to agree to kill Claudio for the insult he has visited upon her cousin, Hero.

Scene 2 is a shorter scene which is set in prison. Dogberry, assisted by Verges and the sexton, interrogates Conrade and Borachio. Although Dogberry is typically inept in his questioning, the sexton grasps the importance of what the prisoners reveal and orders the prisoners to be taken to Leonato. Before they are taken away, Conrade declares that Dogberry is an ass, which causes Dogberry to defend his position with hilarity.