Jacobs was born in Pittsburgh, Pennsylvania, and grew up in Mt. Lebanon, Pennsylvania, a suburb of Pittsburgh.
She made her name locally at the Pittsburgh Public Theater. There she was a perennial contender in the Public's Shakespeare Monologue Contest, which led to her being cast as Titania in its production of A Midsummer Night's Dream. After graduating from Mt. Lebanon High School in 2000, Jacobs moved to New York City, New York, to study acting at The Juilliard School, where she was a member of the Drama Division's Group 33.
Jacobs's first national exposure came in her recurring role as Adele Congreve on the television series The Book of Daniel.
Although she played Kimberly in the television pilot of Traveler, the role was recast when ABC acquired the series.
She subsequently made guest appearances on Law & Order: Criminal Intent and Fringe.
In 2006, Jacobs starred in an Off-Off-Broadway theatre production of Chris Denham's[clarification needed] cagelove. While overall critical reaction to the play was negative, Jacobs earned praise in several reviews. The New York Times advised readers to "make sure to remember the name of Gillian Jacobs, a stunning Juilliard graduate who has the glow of a star in the making".She has also appeared in theatrical productions of The Fabulous Life of a Size Zero (2007) and The Little Flower of East Orange (2008), directed by Philip Seymour Hoffman.
Jacobs's film work includes Gardens of the Night (2007); writer-director Adam Rapp's Blackbird (2007); Choke (2008), based on the Chuck Palahniuk novel, and The Box (2009).
In 2009, she became a regular on Community.
As of early 2010, the film Watching TV with the Red Chinese was in post-production.