Jessie is a prominent member of Team Rocket and the de facto leader of the trio that includes her longtime partners, James and the talking Meowth. Her past is marked by hardship and loss. Her mother, Miyamoto, was a high-ranking Team Rocket agent who disappeared on a mission to find the elusive Pokémon Mew when Jessie was very young. This left Jessie in a poor foster home where she sometimes had to eat snow to survive. Driven by a desire to make something of herself, she attempted several careers before finding her niche. She failed out of a school to become a Pokémon nurse upon realizing the institution was actually for Chansey, not humans. She also studied at a Pokémon technology institute where she first met James, but the pair earned the lowest grades in the school's history. Following this, they joined a bicycle gang, and Jessie also had brief, unsuccessful stints as a weather reporter, a pop idol, a model, and even a ninja.

Possessing a flair for the dramatic, Jessie has a bold, vain, and fiercely ambitious personality. She considers herself a great beauty and an excellent actress who is destined for stardom, and she deeply resents any criticism, especially being called old or having her distinctive magenta hair damaged. She has a famously short temper and can be cruel and competitive, often mocking Ash and his friends. However, beneath her villainous exterior, Jessie possesses a strong sense of loyalty and a genuine, if rarely displayed, capacity for care. This is most evident in her deep bonds with her own Pokémon; she has released several of them, such as her Arbok and Dustox, when she believed it was truly in their best interest to be free.

Jessie's primary role in the narrative is as an antagonist, relentlessly pursuing Ash’s Pikachu as a gift for her boss, Giovanni, the leader of Team Rocket. The trio’s elaborate and often comedic schemes to capture the Pokémon form a staple of the series, and they are regularly sent blasting off after a defeat. In a significant development, Jessie discovered a talent for Pokémon Contests. Disguised under the alias Jesselina in the Sinnoh region, she showcased a more professional and creative side, moving beyond her earlier tendencies to cheat. Her skills as a Coordinator grew substantially, allowing her to win several ribbons and qualify for the Sinnoh Grand Festival, where she proved herself a formidable competitor. She maintains a fierce rivalry with fellow Team Rocket agents Butch and Cassidy.

Jessie’s most significant relationships are with her partners. She and James have a long, complex history that began before Team Rocket, and they share an unbreakable bond, often caring for each other as family. Meowth serves as the trio's translator and a close confidant. Her relationship with Giovanni is more one-sided; while she is fanatically loyal to him and dreams of earning his approval, he often dismisses them. Over the course of the series, Jessie has demonstrated notable growth, transforming from a purely scheming villain into a more nuanced character with genuine skills as a Coordinator and a trainer. Her personal development is often reflected in her journey from using Pokémon as tools to forming deep emotional attachments with them.

As a trainer, Jessie has a preference for snake-like and Poison-type Pokémon. Her notable abilities include piloting various mecha, devising complex capture strategies, and employing a range of disguises. Her team over the years has included Ekans (which later evolved into Arbok and was released), Lickitung (traded for Wobbuffet, who became a permanent and beloved member of the team), Seviper, Yanmega, Dustox (released), and later Pokémon such as Woobat, Frillish, and Mimikyu.