At an early age, Anderson was interested in marine biology, but after becoming interested in theatre during her teenage years, she began acting in high school productions during her first year and later in community theatre. She also served as a student intern at the Grand Rapids Civic Theatre & School of Theatre Arts. After graduating from high school in 1986, she attended The Theatre School at DePaul University in Chicago, where she earned a Bachelor of Fine Arts in 1990. Anderson also participated in the National Theatre of Great Britain’s summer program at Cornell University. To support herself financially during her student years, she worked at the Goose Island Brewpub in Chicago. After Anderson became famous, the brewery named one of their beers after her – a Belgian Style Farmhouse Ale, simply called “Gillian”.

Anderson moved to Los Angeles in 1992 and spent a year auditioning. The same year, she appeared in her first feature-length film, The Turning, starring Karen Allen and Tess Harper. The film drama is an adaptation of the play Home Fires Burning.

Although she had once vowed she would never do television work, being out of work for a year changed her mind. Anderson recalled: “First of all, I swore I’d never move to Los Angeles, and once I did, I swore I’d never do television. It was only after being out of work for almost a year that I began going in [to auditions] on some stuff that I would pray that I wouldn’t get because I didn’t want to be involved in it.” She broke into mainstream television in 1993 with a guest appearance on the collegiate drama, Class of ’96, on the fledgling Fox Network.

Anderson married her first husband, Clyde Klotz, an X-Files assistant art director, on New Year’s Day 1994, in Hawaii in a Buddhist ceremony. Their daughter, Piper Maru, was born on September 25, 1994. Showrunner Chris Carter, Piper’s godfather, named an X-Files episode after her. Anderson and Klotz divorced in 1997. On December 29, 2004, Anderson married Julian Ozanne, a documentary filmmaker, on Lamu Island, off the coast of Kenya. Anderson announced their separation on April 21, 2006. Anderson and former partner, businessman Mark Griffiths, have two children. She ended their relationship in 2012.

In 1996, Anderson narrated the television documentaries Spies Above and Why Planes Go Down. While hosting the BBC documentary series Future Fantastic, she became impressed by the theme music of the show, by the electronic duo Hal and initiated a collaboration with them. In 1997, Anderson provided spoken word vocals and starred in the music video for their single “Extremis”, which was frequently aired on MTV. She also helped to assemble an album of electronic music, Future: A Journey Through The Electronic Underground, for Virgin Records, which won praise from European music critics.

Anderson is a supporter of various women’s organizations and social movements. She has been a long-time supporter of the Feminist Majority Foundation (FMF). In 1996, Anderson became FMF’s spokesperson and participated as a team leader in the FMF’s Million4Roe campaign. In March 1999, she attended an FMF event to stop gender apartheid in Afghanistan and in April 2002, she appeared on Hollywood Squares to benefit the FMF’s campaign to aid Afghan women and girls. Anderson participated in Eve Ensler’s Vagina Monologues, including a stage performance on February 14, 1999. Anderson is a supporter of Ensler’s V-Day movement aiming to end violence against women and girls.

In 1997, Anderson appeared in the independent film Chicago Cab. In 1998, she starred in the film Playing by Heart with Sean Connery, Angelina Jolie, Ellen Burstyn and Jon Stewart. Anderson also had a supporting role in the film The Mighty with Gena Rowlands, Harry Dean Stanton, James Gandolfini and Sharon Stone. In 1999, Anderson had a supporting role in the English-language release of Hayao Miyazaki’s Princess Mononoke, where she voiced the character of Moro. Anderson is a fan of Studio Ghibli and Miyazaki’s work. She also took part in Eve Ensler’s The Vagina Monologues.

As a result of this guest appearance, Anderson was sent the script for The X-Files. She was 24 when she decided to audition because, “for the first time in a long time, the script involved a strong, independent, intelligent woman as a lead character.” Producer Chris Carter wanted to hire her, but Fox wanted someone with previous television exposure and greater sex appeal. Fox sent in more actresses, but Carter stood by Anderson, and she was eventually cast as FBI Special Agent Dana Scully. Anderson got the part assuming it would run for 13 episodes, the standard minimum order for American television networks. Filmed for the first five seasons in Vancouver, British Columbia, before moving to Los Angeles, the series ran for nine seasons. Two related films were also produced, released in 1998 and 2008. During her time on The X-Files, Anderson won numerous awards for her portrayal of Special Agent Scully, including an Emmy Award for Outstanding Lead Actress in a Drama Series, a Golden Globe for Best Actress in a Television Series Drama, two Screen Actors Guild Awards for Outstanding Performance by a Female Actor in a Drama Series and a Saturn Award for Best Actress on Television. Anderson is the first actress to win an Emmy, a Golden Globe, and a SAG Award in the same year. For the role, she received a total of four Emmy nominations, four Golden Globe nominations and nine SAG nominations.

In 2000, Anderson starred in the film The House of Mirth with Eric Stoltz – Terence Davies’ adaptation of the Edith Wharton novel of the same name – for which she won critical acclaim and awards such as the British Independent Film Award for Best Actress, Village Voice Film Poll Best Lead Performance, and a nomination for the National Society of Film Critics Award for Best Actress.

Anderson is an advocate for reproductive rights. In 2001, she emceed the Rock for Choice concert fundraiser, featuring musicians Sarah McLachlan, Paula Cole, and Melissa Etheridge as well as actresses Helen Hunt, Ellen DeGeneres, Portia de Rossi, and Kathy Najimy. The concert supported reproductive options for unplanned pregnancies, including the morning-after pill. For International Women’s Day 2014, Anderson was one of the artist signatories of Amnesty International’s letter to UK Prime Minister David Cameron campaigning for women’s rights in Afghanistan. In March 2015, Anderson backed the Women at the Well drop-in centre for vulnerable women in London, which is supported financially by Comic Relief. Anderson supports the Refuge, a United Kingdom charity providing specialist support for women and children experiencing domestic violence. For International Women’s Day 2016, Anderson was one of the high-profile women that signed Burma Campaign UK’s pledge to end and investigate crimes of sexual violence against girls and women in Myanmar. Anderson is a speaker for Thomson Reuters Foundation’s Trust Women Conference.

When The X-Files ended in 2002, she moved back to London for a complete change of pace and the opportunity to return to the stage. In 2002, Anderson made her West End debut in Michael Weller’s play What The Night Is For at the Comedy Theatre. In 2004, Anderson starred in the Royal Court Theatre’s production of Rebecca Gilman’s play The Sweetest Swing in Baseball, as artist Dana Fielding who assumes the personality of the troubled baseball player Darryl Strawberry – a role for which she earned rave reviews.

In 2005, she appeared as Lady Dedlock in the BBC adaptation of Charles Dickens’ novel Bleak House. She had a starring role in the Irish film The Mighty Celt, for which she won an IFTA award for Best International Actress. The same year she also appeared in A Cock and Bull Story with Steve Coogan and Rob Brydon – a film version of the novel Tristram Shandy. In 2006, Anderson won the Broadcasting Press Guild Television and Radio Award for Best Actress for her role in Bleak House. She was nominated for a British Academy Television Award (BAFTA) for Best Actress, she also received an Emmy nomination for Outstanding Lead Actress in a Miniseries or Movie, a nomination for a Golden Globe, a Satellite Award nomination, and came in second place in the Best Actress category of the 2005 BBC Drama website poll for her portrayal of Lady Dedlock in the adaptation.

While filming The Last King of Scotland in 2005, Anderson started a crowdfunding venture that benefited the Alinyiikira Junior School in Kampala, Uganda. She ran the philanthropic project until 2011. Anderson is a member of the board of directors for Artists for a New South Africa and a campaigner for ACTSA: Action for Southern Africa. She was a patron of the Friends of Treatment Action Campaign (FoTAC) which worked with the Treatment Action Campaign in South Africa to ensure greater access to treatment to reduce the effects of HIV and prevent new infections. Anderson also supported Buskaid – a charitable trust aiming to help young black musicians in South Africa.

During 2006 and 2007, Anderson appeared in two British films: The Last King of Scotland with Forest Whitaker and James McAvoy, (2006) and Straightheads with Danny Dyer (2007). In 2008, Anderson hosted Masterpiece Theatre during the Jane Austen series; she was the first woman to host the series since it began in 1971. The same year, Anderson starred in the second X-Files film, The X-Files: I Want to Believe and appeared alongside Simon Pegg in the British comedy film How to Lose Friends & Alienate People. In 2009, she starred in the British comedy film Boogie Woogie with Alan Cumming, Danny Huston and Stellan Skarsgård.

In 2008, Anderson co-founded South African Youth Education for Sustainability (SAYes), which helps in empowering marginalised young people in South Africa through youth mentoring. The nonprofit organization provides youth leaving children’s homes with guidance that enables them to develop their skills, further their education, and source suitable housing in order to participate in society as independent adults.

She portrayed Nora in Ibsen’s A Doll’s House at the Donmar Warehouse in London’s West End during a limited engagement which ran from May 14, 2009, until July 18, 2009. Anderson received a nomination for the Laurence Olivier Award for Best Actress, for productions which opened in the 2009 calendar year, for her portrayal of Nora.

In 2009, Anderson was named as one of 20 most powerful women in British theatre and was dubbed “The Honorary Brit” by Harper’s Bazaar and Tiffany & Co.’s list. In 2010, Anderson was named Honorary Associate of The London Film School (LFS).

In November 2010, Anderson portrayed Wallis, Duchess of Windsor in Any Human Heart – a television adaptation of William Boyd’s novel of the same name, for which she was nominated for a BAFTA for Best Supporting Actress on Television. In April 2011, she starred in the BBC adaptation The Crimson Petal and the White as Mrs. Castaway, for which she was nominated for the Broadcasting Press Guild Award for Best Actress. In August 2011, she appeared in the television miniseries Moby Dick based on Herman Melville’s 1851 novel, as Elisabeth, Ahab’s wife. The same year, Anderson appeared as the head of MI7, Pamela Thornton, in the British comedy Johnny English Reborn. She starred as Miss Havisham in a three-part BBC adaptation of Great Expectations that aired in late December 2011. For her portrayal in the adaptation she won the Artistic Excellence Award, was nominated for the Critics’ Choice Television Award for Best Actress in a Movie/Miniseries and for the Broadcasting Press Guild Award for Best Actress.

In late 2010, Anderson and other artists joined a campaign to boycott Botswana diamonds over the government’s treatment of the Kalahari San. Anderson supports tribal rights charity Survival International, an organization that champions tribal peoples around the world and in early 2010 she participated in a performance in a London stage fundraiser for its cause. In February 2011, Anderson narrated a short film about recent footage of an uncontacted tribe, in which the Amazon Indians were spotted from the air on the Brazil-Peru border. Anderson has said: “What comes across powerfully from this amazing footage is how healthy and confident these people appear. I hope they can be left alone – but that will only happen if the loggers are stopped.” In June 2011, Anderson became an ambassador for Survival International. In September 2015, Anderson was among the artists who signed a letter calling for a new approach to conservation that would respect tribal peoples’ rights.

Anderson is the eldest of three siblings. Her brother Aaron – who was diagnosed with neurofibromatosis – died in 2011 of a brain tumor, at the age of 30. Aaron was a DJ, a mentor, and a practicing Buddhist. He was in his second year of a PhD program in developmental psychology at Stanford University when he was diagnosed with glioblastoma in 2008. Her sister Zoe is a ceramicist, whom Anderson calls “an exceptional artist”. Zoe is openly gay and is married to her partner.

Anderson is an honorary spokesperson for the Neurofibromatosis Network. She often holds auctions with the profits benefiting the NF Network. Her brother Aaron died from the disease in 2011. In May 1996, Anderson addressed the United States Congress urging for more education and funding for NF research projects. She partners with Doodle 4 NF – an annual fundraiser for the NF Network. She also supported the Children with Tumours organization and the Global Genes movement, which is devoted to helping children with NF.

In 2012, Anderson appeared in a Swiss drama film, Sister, and in Shadow Dancer – a British-Irish drama film based on the novel of the same name, about the Irish republican movement. Anderson voiced the character of Dr. Miki Hokuto in the English-language version of Studio Ghibli’s From Up on Poppy Hill, which was released in March 2013. The same year, she starred in the Canadian techno-thriller I’ll Follow You Down and appeared in Mr. Morgan’s Last Love with Michael Caine.

In March 2012, Anderson told Out magazine about her past relationships with women. Anderson identifies as heterosexual. In an interview with the London Evening Standard in December 2014, she stated: “I am an actively heterosexual woman who celebrates however people want to express their sexuality.” In an interview with The Daily Telegraph in March 2015, Anderson said that she was not closed to the idea of entering another same-sex relationship, adding: “To me a relationship is about loving another human being; their gender is irrelevant.”

In 2012, Anderson joined Greenpeace in standing with the people of Brazil for a zero-deforestation law to save the Amazon. In 2013, she backed the Cheetah Conservation Fund by creating a short film together with the fund, advocating CCF’s action to prevent the extinction of the cheetah. In 2013, she joined the Fishlove campaign, supporting the fight against unsustainable fishing practices that harm the marine ecosystem. In November 2015, Anderson was named a friend and supporter of Positive Luxury, a company that informs consumers on brands’ commitment to quality, craftsmanship, service and sustainability.

Anderson is bidialectal. With her English accent and background, she was mocked and felt out of place as a teenager in the American Midwest and soon adopted a Midwestern accent. To this day, she easily shifts between her American and English accents. In May 2013, during an interview with BlogTalkRadio, Anderson addressed the matter of her national identity: “I’ve been asked whether I feel more like a Brit than an American and I don’t know what the answer to that question is. I know that I feel that London is home and I’m very happy with that as my home. I love London as a city and I feel very comfortable there. In terms of identity, I’m still a bit baffled.”

In May 2013, Anderson began starring as DSU Stella Gibson in The Fall, a critically acclaimed crime drama series for BBC Two and RTÉ One. Anderson was praised for her portrayal of the cool, self-assured Gibson, and was nominated for several awards. She also became an executive producer for the programme from its second series. Between 2013 and 2015, Anderson played Dr. Bedelia Du Maurier, Hannibal Lecter’s psychiatrist, on the NBC series Hannibal. In 2014, Anderson was promoted from a recurring character during the first two seasons, to a series regular for the third season. In 2014, Anderson starred in the British independent science fiction film Robot Overlords alongside Sir Ben Kingsley. That year, she also appeared in Jeffrey D. Brown’s drama Sold, portraying Sophia, a character based on the humanitarian photographer Lisa Kristine. The film presents the issues of child trafficking and sexual slavery in India, and is based on Patricia McCormick’s novel of the same name.

Anderson has been active in supporting numerous charity organizations, global and social causes, as well as running her own humanitarian ventures. She supports The Trevor Project organization, focused on suicide prevention efforts among LGBTQ youth and attended three of the Trevor Project’s “Cracked X-Mas” events to benefit the organization. In 2013, Anderson was made a patron of the Charles Dickens Statue Fund, and was instrumental in securing the funding for UK’s first Dickens statue, located in Portsmouth, Hampshire. In June 2016 she became a patron of the Temple Legal Centre, a London-based organization that assists people through the legal process by providing them free family law advice and support. In June 2016, Anderson expressed her support for the United Kingdom to remain a member of the European Union in the run-up to June’s referendum on that issue. In January 2018, Anderson was given a City Lit Lifetime Fellowship Award by the adult education college City Literary Institute.

In July 2014, Anderson gained critical acclaim for her stage performance as Blanche DuBois in A Streetcar Named Desire by Tennessee Williams at the Young Vic Theatre in London. She won the Evening Standard Theatre Award for Best Actress and received her second Laurence Olivier Award nomination for Best Actress. The production became the fastest-selling show in the theatre’s history, and the run was extended by two weeks due to the demand for tickets. In the first collaboration between the Young Vic Theatre and National Theatre Live, the show was broadcast live to over 1100 venues on September 16, 2014. Thus far, it has been screened in more than 2000 venues. In February 2015, Anderson directed and starred in a short film prequel to A Streetcar Named Desire, titled The Departure, written by novelist Andrew O’Hagan. This is part of the Young Vic’s short film series, which is produced in collaboration with The Guardian.

In October 2014, Anderson published her first book, A Vision of Fire, co-authored with Jeff Rovin. The book is the first novel of what has developed as The Earthend Saga trilogy. The publisher describes it as “a science fiction thriller of epic proportions”. In December 2015, Anderson and Rovin published their second novel of the trilogy, A Dream of Ice. In January 2016, Anderson portrayed Anna Pavlovna Scherer in BBC One’s television adaptation War & Peace. The same month, she returned to portray FBI Special Agent Dana Scully in the six-episode tenth season of The X-Files. Anderson has fought and succeeded in securing equal pay with her male co-star on The X-Files in the ’90s and again in 2015, when negotiating her salary with the network. She has been outspoken about the ongoing issue throughout the years.

Anderson is a patron of Childreach International, a London-based charity that works in partnership with local communities in the developing world to secure children’s basic rights; she addressed the problem of child trafficking during the press for the Sold film that presents the issue. Anderson also supports their Taught Not Trafficked campaign that was launched in July 2014. In 2015, Anderson became a patron of the International Literacy Centre (ILC) – European home of Reading Recovery. In January 2016 she helped launch ILC’s Reading Recovery Read Aloud campaign. During February and March 2016, Anderson held an internet charity auction benefiting Great Ormond Street Hospital (GOSH) children’s hospital in the Bloomsbury area of London. In March 2016, it was reported that Anderson is one of the artists sponsoring an unaccompanied refugee minor in the “Jungle” camp in Calais. In July 2017, Anderson was awarded a UCL Honorary Fellowship for her support of the International Literacy Centre’s Reading Recovery program.

From April 23, 2016 through June 4, 2016, Anderson reprised her role of Blanche DuBois in A Streetcar Named Desire on stage at the new St. Ann’s Warehouse in Brooklyn, New York City. On September 13, 2016, Anderson and Rovin published The Sound of Seas; their third and final novel of The EarthEnd Saga trilogy. The same month, she returned to portraying DSU Stella Gibson in the third series of The Fall. Anderson is the narrator of the English dub of Ronja the Robber’s Daughter – Studio Ghibli’s anime, which began streaming on Amazon Prime in January 2017. In February 2017, Anderson portrayed Edwina Mountbatten in Gurinder Chadha’s Partition drama film Viceroy’s House (2017).

In 2016, Anderson was appointed an honorary Officer of the Most Excellent Order of the British Empire (OBE) for her services to drama. In 2018, she received a star on the Hollywood Walk of Fame.

On March 7, 2017, Anderson and the journalist-activist Jennifer Nadel published their self-help guide book for women, titled WE: A Manifesto for Women Everywhere. Anderson stated that the book is a “call-out to all women around the world – and by women I include girls, transgender, anyone who identifies themselves as being intrinsically female.” In April 2017, she played goddess Media in the first season of American Gods – a television series adaptation of Neil Gaiman’s science fiction novel of the same name. Following the departure as showrunners of the show’s creators, Bryan Fuller and Michael Green, Anderson stated she would not return to the show. In October 2017, Anderson appeared alongside Glenn Close and Christina Hendricks in Crooked House – a film adaptation of Agatha Christie’s novel of the same name. In January 2018, she was back playing FBI Special Agent Dana Scully in the eleventh season of The X-Files. In January 2018, she confirmed that she would be leaving The X-Files after the end of the season. Anderson is set to portray the role of Captain MacLaren in Star Citizen’s single-player component Squadron 42. In January 2019, she began playing Jean Milburn in the Netflix dramedy Sex Education.

From February 2, 2019 through May 11, 2019, Anderson portrayed Margo Channing in a stage production of All About Eve at the Noël Coward Theatre for which she received her third Laurence Olivier Award nomination. On September 7, 2019, it was officially announced that she will portray former British Prime Minister Margaret Thatcher in the fourth season of the Netflix historical drama series The Crown. Anderson will become the second American actress (after Meryl Streep in The Iron Lady) to portray Thatcher in a major production. In a statement Anderson said: “I am so excited to be joining the cast and crew of The Crown and to have the opportunity to portray such a complicated and controversial woman, Thatcher was undoubtedly formidable but I am relishing exploring beneath the surface and, dare I say, falling in love with the icon who, whether loved or despised, defined an era.”