Hilary is the oldest daughter of the Banks family. In the earlier seasons, Hilary's snobbishness is emphasized, as well as her shallow trendy environmental activism. She is best described as impulsive, shallow, attractive, most of the time very dim-witted and extremely self-centered, who can come off as a very arrogant airhead; she looks down on Will's upbringing and is obsessed with shopping and money. However, despite her apparent shallow personality, she has a strong sense of integrity and shows obvious affection for her family members. Will gets along with her better than with Carlton. She is stereotyped as a mean girl.
She is often portrayed as having no common sense.
During the series, Hilary attends and drops out of UCLA, after which she begins a long streak of luck that eventually lands her a nationally-televised daytime talk show titled "Hilary." Her television career begins when she becomes a weather girl at a local TV station. She meets and falls in love with Trevor Collins (portrayed by Brian Stokes Mitchell). However, Trevor dies in a bungee jumping accident while proposing officially to Hilary. She wanted to have everyone know they were getting married in a big way. After Trevor dies, she fleetingly feels guilt for having caused his death with her demand of a big proposal.
Hilary's career thrives, with her show getting national broadcast, but she still feels empty inside and fundamentally depressed. However, this seems to change when a woman goes into labor on Hilary's show (she was doing a segment on pregnant women). Hilary feels joy when she holds the newborn in her arms. The experience pushes Hilary into thinking she wants a baby, although Philip was deadset against it unless she married a man. Her wish to become a mother has her consider getting a sperm donor (something she gives up on when she finds out the donor is Jazz) and to go on a date with someone to whom she isn't exactly attracted. Eventually, Phil manages to convince her that happiness must come from inside her, not out of shopping and luck.
At the conclusion of the series, Hilary's talk show moves to New York City, as does most of the rest of the Banks family. Hilary's hair styles have changed as the series progressed; early in the series it was brown with tight curls, it then became longer and curly with blonde highlights, but later it was black, straight, and shoulder-length.
Trevor and Hilary work on the same TV station: he is a reporter, she's a weather girl. They fall in love after one date, and the relationship quickly gets serious: in "When There's A Will, There's A Way (Part 1)", Hilary comes downstairs dressed as a bride and announces to Phil, Will and Carlton that she's engaged to Trevor, Trevor having proposed that morning while leaving the poolhouse (realizing her father has no idea she was sneaking him in, she quickly corrects saying he proposed while on the phone with her).
Hilary talks Trevor into proposing to her in a major way, what he decides to do live on TV in a live-televised bungee-jumping stunt. The whole family gathers to watch it; however, it ends tragically when Trevor has an accident and smashes on the ground. Trevor dies because of this, and Hilary feels guilty for it, since it was her demand of having a big proposal that led to his death. The last thing he said was "Hilary Banks will you marry...."
When first meeting her cousin, she thinks nothing of him and asks her father for $300 dollars. They seem to have a classic sibling rivalry, which was most prominent in "Knowledge Is Power" when she rats Will out for coming in the house at 3 in the morning. Will retaliates by blackmailing her with knowledge of her college dropout. However after Will gets shot, they get along with one and other just fine. It extends all the way to the end of the show when Hilary offers Will a job on her talk show when it moves to New York.
- Hilary is portrayed as a stereotypical valley girl and speaks with some strong val-speak habits, in spite of her disdain for the San Fernando Valley (as evidenced from when she said, "And hell is like, the Valley.")