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." 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 19.After beginning her career on stage, Anderson achieved international recognition for her role as FBI Special Agent Dana Scully on the American sci-fi drama series The X-Files.Her film work includes the dramas The Mighty Celt (2005), The Last King of Scotland (2006), Shadow Dancer (2012), Viceroy's House (2017) and two X-Files films: The X-Files: Fight the Future (1998) and The X-Files: I Want to Believe (2008).
In May 2013, during an interview with Blog Talk Radio, 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.
After Anderson became famous, the brewery named one of their beers after her – a Belgian Style Farmhouse Ale, simply called "Gillian". 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.
Aside from film and television, Anderson has taken on the stage and received both awards and critical acclaim.
Her stage work includes Absent Friends (1991) – for which she won a Theatre World Award for Best Newcomer, A Doll's House (2009) – that earned her a Laurence Olivier Award nomination, and a portrayal of Blanche Du Bois in A Streetcar Named Desire (2014, 2016) – for which she won the Evening Standard Theatre Award for Best Actress and received her second Laurence Olivier Award nomination for Best Actress.