Hewitt began her career as a child actress and singer, appearing in national television commercials before joining the cast of the Disney Channel series Kids Incorporated (1989–1991).

[6] She attended Lincoln High School[16] where her classmates included Jonathan Neville, who became a talent scout and recommended Hewitt for her role in Party of Five.

[17] Her first break came as a child actress on the Disney Channel variety show Kids Incorporated (1989–1991),[18] which earned her, as a member of the cast, three Young Artist Award nominations.

Workout with Barbie (1992), which was released by Buena Vista,[19] and obtained her first feature film role in the independent production Munchie, in which she played Andrea, the love interest of a bullied young boy.

[20] A year later, she had her first starring role in Little Miss Millions, as a wealthy nine-year old who runs away from her stepmother to find her real mother, and appeared as a choir member in Sister Act 2: Back in the Habit.

[25] Hewitt rose to teen idol status after landing the role of Sarah Reeves Merrin on the popular Fox show Party of Five (1995–99).

[30] She was cast in the role based on her "ability to project vulnerability," which the producers, director Jim Gillespie, and writer Kevin Williamson unanimously agreed upon.

While the film received mixed reviews, an Entertainment Weekly columnist praised Hewitt's performance, noting that she knows how to "scream with soul".

[35] Hewitt starred as Amanda Beckett, the most popular girl in school and the senior class prom queen, in the teen comedy Can't Hardly Wait (1998).

[36] Critic James Berardinelli asserted that Hewitt was "so likable that it's hard not to have at least a minor rooting interest" in her character,[37] and with a US $25.6 million gross at the North American domestic box office, the film emerged as a moderate commercial success.

[38] Telling You, another 1998 teen comedy, featured Hewitt as the annoyingly sweet ex-girlfriend of a college student working in a pizza joint.

In 1999, she played a record company executive in the independent comedy The Suburbans and starred in and produced Time of Your Life, a Party of Five spin-off following her character as she moved to New York City to learn more about her biological parents.

[44] Hewitt starred alongside Sigourney Weaver in the romantic comedy Heartbreakers (2001), playing a mother-daughter team setting up an elaborate con to swindle wealthy men out of their money.

[48] Hewitt starred as a genius scientist with aspirations of field work, alongside Jackie Chan, in the action comedy The Tuxedo (2002).

[49] Robert Koehler of Variety noted that Hewitt "has displayed a Chan-like sweetness herself in past roles" and was disappointed that her character is "a haggling, high-strung shrew who's instantly repellent" rather than an amusing sidekick as Chan has had in other Hollywood films.

[52] In 2004, Hewitt starred as a musician in the romantic fantasy drama If Only, the love interest of Ebenezer Scrooge in the television film A Christmas Carol, and Dr. Liz Wilson in the live-action comedy Garfield.

[58] In 2005, she played a happily married English woman in the romantic comedy The Truth About Love, and a 28-year-old advertising executive more concerned with being a well-known socialite than being a good person in the television film Confessions of a Sociopathic Social Climber.

Hewitt reprised her role as Dr. Liz Wilson for Garfield: A Tail of Two Kitties (2006),[59] which, though it did not perform as well as its predecessor, achieved a strong box office gross.

[61] In 2008, she made a cameo appearance in the successful action comedy Tropic Thunder, and reunited with Freddie Prinze Jr. in the animated production Delgo which, when released, was a massive box office bomb,[62] taking in US $694,782 in North America.

[69] While reviewers unanimously praised White's performance, Variety wrote: "The same can hardly be said of Hewitt, who —in her current TV movie phase— was put to better use as a mom turned hooker in Lifetime's The Client List.

[71] In 2012, Hewitt starred as the love interest of a gentile pretending to be Jewish, alongside Ivan Sergei and Joel David Moore in the independent comedy Jewtopia,[72] and played an erotic masseuse in the television series The Client List.

Between 2014 and 2015, Hewitt played the regular role of Kate Callahan, an undercover agent who joins the Behavioral Analysis Unit (BAU), in the tenth season of Criminal Minds.

'"[28] Beginning in 2018, Hewitt has played Maddie Buckley, an ER nurse working as a 9-1-1 operator after leaving an abusive relationship, on the Fox police procedural 9-1-1.

[95] Since 2004, Hewitt has remained mostly inactive in the music industry, but she released the compilation albums Cool with You: The Platinum Collection (2006) in Asia and Hey Everybody (2007) in Brazil.

[100] While promoting the book during a January 2010, interview on Lopez Tonight, Hewitt said that there is a chapter in it about "vajazzling" (decorating a woman's pubis with crystals or rhinestones).

As noted by Elle magazine, it was "bequeathed" to her around the time she turned 18 and starred in I Know What You Did Last Summer (1997) and Can't Hardly Wait (1998), roles which, along with Party of Five, "cemented her status as an icon to a whole generation.

[111] Hewitt graced the February 1997 cover of Seventeen, and in subsequent years, the list went on to include Rolling Stone, Cosmopolitan, GQ, CosmoGirl, Shape, Health, Maxim, FHM, Vanidades and Jane.

[112] Hewitt has appeared in numerous print advertisements and commercials for brands such as Victoria Golf, Mrs. Smith's, Colonial's Iron Kids Bread, Levi's, Barbie, LA Gear, Chex, Proactiv, Hanes, Neutrogena, Nokia, JanSport and America's Dairy Producers.

[citation needed] Between the 1990s and the 2000s, Hewitt dated several high-profile figures, including Joey Lawrence, Will Friedle, Carson Daly, Rich Cronin, Patrick Wilson, John Mayer and Jamie Kennedy.

[132][133] After almost a year of involuntary commitment and prison, Napolis pleaded guilty and was released on probation with a condition that she was barred from any contact with both Spielberg and Hewitt.