In The Merchant of Venice, Nerissa is witty, strong-willed and manipulative. She is also smart, level-headed, and loyal to her mistress, Portia. Since Portia has become an orphan, Nerissa has in many ways been more a friend than a servant. She offers a sounding board for Portia to express her opinions about the courtship process and the shortcomings of the specific suitors, but judiciously advises her to follow her father’s will. Because Nerissa hopes to remain in Portia’s employ, she is concerned to help her mistress choose a husband who will be a good boss for her as well. But because she is also a young, single woman, Nerissa has her eyes open for a likely prospective husband for herself, and finds one in Gratiano.

Nerissa’s loyalty to Portia merges with her strong will when she joins her is donning a man’s disguise. As Portia is the lawyer, she is the law clerk. Although she is not speaking before the court as her mistress is, Nerissa is bodly impersonating a man so that she can accompany Portia in this bold endeavor.

Nerissa’s combined wit and skill at manipulation become most evident in the ring episode after Act IV’s trial scene. She tells Portia "we'll outface them, and outswear them too." Still in disguise, she requests that Gratiano give “him” his wedding ring. Dismayed that he so easily set aside his vow, she figures out how to gain revenge—by pretending that she had sex with the clerk, which was how he got the ring. Gratiano is suitably shamed, and the audience suspects he will become a devoted husband.