Jacobs' first acting role came as Adele Congreve on the television series The Book of Daniel. Although she played Kim in the pilot of Traveler, the role was given to Pascale Hutton when ABC acquired the series. Jacobs subsequently made guest appearances on Law & Order: Criminal Intent and Fringe. In 2006, she starred in an Off-Off-Broadway production of Chris Denham's cagelove. While overall critical reaction to the play was negative, Jacobs earned praise in several reviews.The New York Times advised readers to "remember the name of Gillian Jacobs, a stunning Juilliard graduate who has the glow of a star in the making".
Jacobs has appeared in theatrical productions of The Fabulous Life of a Size Zero (2007), A Feminine Ending (2007), and The Little Flower of East Orange (2008). Her film work includes Gardens of the Night (2007), Blackbird (2007), Choke (2008), and The Box (2009). In 2009, she began playing Britta Perry on Community, which became her best known role to date.
^"Purple Editorial A New Generation, Spring/Summer 2009". Gillian Maclaren Jacobs's Portfolio. My Fashion Database. Spring–Summer 2009. Retrieved 22 July 2012. "What's your full name? - Gillian Maclaren Jacobs ... What are your parents' names? - Martina Magenau Jacobs and William F Jacobs Jr"