She made her screen debut with a guest appearance on the American soap opera All My Children (1995), and voicing Betty Ann Bongo on the Nickelodeon cartoon series KaBlam!

She appeared in major pictures such as the romantic comedy Notting Hill (1999) and M. Night Shyamalan's psychological thriller The Sixth Sense (1999).

Barton has since appeared in the comedy remake St Trinian's (2007), the Richard Attenborough–directed drama Closing the Ring (2007) and Assassination of a High School President (2008).

[10] Barton graduated from the Professional Children's School in Manhattan in 2004, and took a summer short course called Acting Shakespeare at The Royal Academy of Dramatic Art in London, in June and July 2006,[11] at Sir Richard Attenborough's urging,[12] after he directed her in Closing the Ring.

[15] She appeared in several other Off-Broadway productions, taking a lead role in James Lapine's Twelve Dreams alongside Marisa Tomei at Lincoln Center.

The New York Times also remarked that "the winning child actresses Brittany Boyd and Mischa Barton are already smart enough not to overplay the naivete and precocity of their respective characters.

[22] She guest-starred in eight episodes of the television series Once and Again as Jessie Sammler's (Evan Rachel Wood) girlfriend, Katie Singer.

In 2001, she returned to film and starred in the independent Canadian drama, Lost and Delirious, based on the novel The Wives of Bath by Susan Swan.

The film was met with mixed reviews, but the performances of Barton and her co-stars Piper Perabo and Jessica Paré were widely praised.

[23] She also starred in Julie Johnson (2001) alongside Lili Taylor and Courtney Love, playing the daughter of a woman in a lesbian relationship.

[25] In August 2003, Fox premiered the television series The O.C., about affluent teenagers with stormy personal lives who reside in scenic Orange County, California.

The show became an overnight success due to its large fanbase, and resulted in Barton's fame being increased through her role as Marissa Cooper.

[27] In July 2006, Barton appeared on the British comedy variety show The Friday Night Project as a guest host.

She appeared in Assassination of a High School President (2008), co-starring Bruce Willis, which premiered at the 2008 Sundance Film Festival.

[36][37] She guest starred on Law & Order: Special Victims Unit, played an endangered prostitute in an episode that aired on 3 March 2010.

Writing in the Los Angeles Times, Katie Walsh described how "Barton is a standout as the alluring, broken young woman who hides as much as she reveals.

[57] Barton had a cameo appearance in Spree, which starred Joe Keery of Stranger Things and premiered at the 2020 Sundance Film Festival.

[58] In October 2021, Barton was tapped to play an aspiring detective Miranda Green in the crime thriller film Invitation to a Murder, directed by Stephen Shimek.

[59] In April 2023 it was announced that Barton would be a guest star in the rebooted Australian soap opera, Neighbours on Amazon Freevee and Australia's Network 10.

[63] In Australia, she appears in commercials for teen magazine Famous and was the guest of honour at retail giant David Jones Tahitian Summer Collection launch.

[72] In addition, she lent her name to the TRAID campaign (Textile Recycling for Aid and International Development) in association with Visa Swap.

[73] Barton was photographed in April 2007 for the Fall 2007/2008 advertising campaign for Italian clothing brand Iceberg, modelling with Nicolas Bemberg.

[80][81] In October 2011, Barton appeared in a meat-themed photoshoot for Tyler Shields that was showcased at the Imitate Modern Gallery in London.

[82] In 2012, Barton opened a short-lived clothes boutique in Spitafields, London, later revealing “Retail is not exactly a cakewalk, so just taking care of the store and dealing with production, quality and employees.

[85] She was previously in long-term relationships with the oil heir Brandon Davis, musician Cisco Adler, and the Australian model James Abercrombie.

[86][87][88] In 2017, Barton won a revenge porn lawsuit against her former boyfriend, Jon Zacharias, stopping him from selling a sex tape of her.

creator Josh Schwartz later said that "Mischa was one of the young women stalked by photographers and treated unkindly by online bloggers.

[92] Barton wrote in Harper's Bazaar in 2021 that she felt that she had been "sexualised" in her earlier film roles, even becoming a "strange sex symbol" at 13 in Asia where her movie Pups garnered significant attention.

[93] In 2023, an article from 2005 circulated in which Barton stated a Hollywood publicist told her to sleep with Leonardo DiCaprio when she was just 18 years old in order to benefit her career.

[94] In 2009, Barton served as the spokesperson for Climate Star, an organization that fights global warming through social and legislative activism.