The eponymous but nameless Duchess is the main protagonist, loosely inspired by Giovanna d’Aragona, Duchess of Amalfi. She begins the play as a widowed woman who oversees the Malfi court. Though the Italian courts are full of flatterers and panderers, the Duchess herself is kind, gentle, and virtuous. Though her twin, Ferdinand, and their brother, the Cardinal, do not want the Duchess to remarry, she wants a second marriage made for love. She secretly marries her household steward, Antonio. Over the course of the play’s first half, they have three children.

The Duchess is notable among the heroines of early modern drama due to the active role she takes in shaping her future, even if she must deceive to do so. While Antonio has reservations about their marriage, the Duchess pursues him with clear romantic intent. In one of the play’s most romantic scenes, she removes her wedding ring and puts it on Antonio’s finger, claiming it will provide the physic he needs. She then says that only her husband is destined to wear that ring, which serves as a lead-in to her bold proposal of marriage.

Though the Duchess initially keeps her family a secret, she also protests her unfair treatment.