She had a leading role in the short-lived teen drama series Swans Crossing (1992), which was followed by her breakthrough as Kendall Hart on the ABC soap opera All My Children (1993–1995), for which she won a Daytime Emmy Award.

In television, Gellar headlined The CW's Ringer (2011–2012), CBS's The Crazy Ones (2013–2014), and Paramount+'s Wolf Pack (2023), as well as providing voice work for Robot Chicken (2005–2018), Star Wars Rebels (2015–2016), and Masters of the Universe: Revelation (2021).

[16] With her single mother working "just above the poverty line",[17] Gellar received a partial scholarship to study at the Columbia Grammar & Preparatory School, where she experienced bullying.

[30] Executives at McDonald's parent company were so enraged that they sued all parties involved, naming Gellar and reportedly banning her from eating at the food chain.

[38][39][40] Gellar appeared in a safety skit during the November 11, 1985 episode of Late Night with David Letterman,[41] and guest starred in various television series, such as Spenser: For Hire and Crossbow.

[44] Gellar portrayed 13-year-old Mollie in the initial production of Neil Simon's play Jake's Women, which ran at the Old Globe Theatre in San Diego, California, from March to April 1990.

Gellar obtained her first leading role, as a mayor's manipulative daughter, in the 1992 syndicated teen serial Swans Crossing, which chronicled the lives of a group of wealthy teenagers.

She felt that playing a "villainous" character gave her the call for "better and more varied acting skills", while the gig's weekly payment proved a financial aid for Gellar and her mother.

[46] Gellar made her debut on the ABC soap opera All My Children in 1993, playing Kendall Hart, the long-lost teenage daughter of character Erica Kane (Susan Lucci).

[25] Gellar's cameo as a girl sitting in the high school cafeteria in the sleeper hit She's All That (1999)[75] was soon followed by her first top-billing film role, as a struggling restaurant owner, in the romantic comedy Simply Irresistible (1999).

[79] In Roger Kumble's Cruel Intentions (1999), a modern-day retelling of Les Liaisons dangereuses, Gellar portrayed Kathryn Merteuil, a cocaine addict with an appetite for manipulating people.

[80] In his review for the film, Ebert felt that she is "effective as a bright girl who knows exactly how to use her act as a tramp",[81] and in an interview with Chicago Tribune, Kumble described her as "the most professional actor I ever worked with".

Her next film, James Toback's independent drama Harvard Man (2001),[89][90][91] in which she starred as the "sharp and shrewd" daughter of a mobster,[92] helped her shed her good girl image, along with Cruel Intentions, according to Peter Travers of Rolling Stone.

[94] Despite negative reviews, A. O. Scott of The New York Times felt that her performance added "a snarl of Powerpuff feminism to her character's ditzy stereotype",[95] and with a global gross of US$275 million,[96] Scooby-Doo emerged as Gellar's most widely seen film to date.

[98] With Jack Black, she hosted the 2002 MTV Movie Awards, which attracted 7.1 million viewers on its June 6 broadcast, achieving the show's highest rating ever at the time.

[121] In 2006, Gellar briefly reprised the role of Karen in the sequel The Grudge 2,[122][123][124] and starred in Asif Kapadia's psychological thriller The Return, as a businesswoman haunted by memories of her childhood and the mysterious death of a young woman.

"[137] The psychological thriller Possession, in which Gellar starred as a lawyer whose life is thrown into chaos after a car accident sends her husband and brother-in-law into comas, had a range of release dates in the United States between 2008 and 2009, due to financial problems at Yari Film Group.

[141] Gellar took a two-year hiatus from acting following the birth of her daughter in 2009, and in 2011, she signed to star and work as executive producer for The CW's Ringer, in which she played the dual role of twin sisters, one of whom is on the run and manages to hide by assuming the wealthy life of the other.

[160][161] Digital Spy felt that Williams "shares a warm, genuine chemistry with his on-screen offspring Gellar,"[162] as part of a mixed critical response.

[166] In Veronika Decides to Die,[167][168] Gellar starred as a young depressed woman who rediscovers the joy in life when she finds out that she only has days to live following a suicide attempt.

[173] Following the conclusion of The Crazy Ones and the death of Williams, Gellar took another sabbatical from screen acting, stating that she had "been working [her] entire life" and "needed that break" to focus on raising her children.

[184] Mark Donaldson of Screen Rant described them as "low-key return movies" for Gellar, noting Clerks 3 as "a nod" to having previously worked with Smith, and Do Revenge as a reassessment of Cruel Intentions for "modern audiences".

[185] At the 2022 San Diego Comic-Con, it was announced that Gellar would star in and act as an executive producer of the Paramount+ supernatural drama series Wolf Pack, which premiered on January 26, 2023.

[189][188] With Project Angel Food, she delivered healthy meals to people infected with AIDS, and through the Make-A-Wish Foundation, she granted sick children's wishes of meeting her while working on Buffy.

After her February 1998 appearance on Seventeen,[199] the list went on to include Nylon, Marie Claire, Vogue, Glamour, Esquire, Allure, Cosmopolitan, FHM, Rolling Stone, and Elle, among others.

[205][206] In October 2015, Gellar, along with entrepreneurs Galit Laibow and Greg Fleishman, co-founded Foodstirs, a startup food crafting brand selling via e-commerce and retail easy-to-make organic baking mixes and kits for families.

"[212] Writing for Bloody Disgusting, Alex DiVincenzo asserted that "Buffy the Vampire Slayer alone should be enough to cement her horror icon status", and highlighting some of her roles in the genre, observed: "Regardless of whether they made it to the end credits, her characters were intelligent, resourceful, and empowering.

In 1999, she signed on to be the face of Maybelline —becoming the company's first celebrity spokeswoman since Lynda Carter in the late 1970s—[216][217] and was voted number one in FHM's "100 Sexiest Women" of the year.

[220] In 2002, Gellar was honored with a Woman of the Year Award by Glamour magazine,[221] and her wax figure by Madame Tussauds, was unveiled as part of the "Trail of Vampires" exhibition.

[231] They were engaged in April 2001 and married in Mexico on September 1, 2002,[232] in a ceremony officiated by Adam Shankman, a director and choreographer with whom Gellar had worked on Buffy the Vampire Slayer.