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 freshman year and later in community theatre.
To support herself financially during her student years, she worked at the Goose Island Brewpub in Chicago.
Anderson is the co-writer of The Earth End Saga novel trilogy and the self-help guide book WE: A Manifesto for Women Everywhere.
Anderson has been active in supporting numerous charities and humanitarian organizations.
Among other honours, Anderson has won a Primetime Emmy Award, a Golden Globe Award and two Screen Actors Guild Awards.
She has lived in London since 2002, after earlier years divided between this city and places in the United States.
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.
She was voted by her classmates as "class clown", "most bizarre girl" and "most likely to be arrested".
She was, in fact, arrested on graduation night for breaking and entering into her high school in an attempt to glue the locks of the doors.
He was in his second year of a Ph D program in Developmental Psychology at Stanford University when he was diagnosed with glioblastoma in 2008.
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.
Aside from film and television, Anderson has taken on the stage and received both awards and critical acclaim.