Olivia Thirlby grew up in New York City, where she is still living. She learnt acting in the American Globe Theatre and in the London Royal Academy of Dramatic Art. In 2003, she debuted in stage plays. She had her first film role in the drama United 93 from 2006. In the drama Snow Angels (2007) she was seen beside Kate Beckinsale. In the comedy Juno (2007) she played the friend of unintentionally pregnant Juno MacGuff (Ellen Page). Her first bigger role was beside David Duchovny in The Secret.