Born and raised in New York City, Thirlby attended Friends Seminary trained at the American Globe Theatre, as well as the Royal Academy of Dramatic Art in London. She completed a stage combat course with the British Academy of Stage and Screen Combat (BASSC).

In 2003, while still at high school, she was offered a role in The Secret. She has expressed an interest in pursuing a career in professional theatre.

In addition to Juno, Thirlby has appeared in United 93 and Snow Angels. She also played "Aubrey" on Kidnapped. She has a number of films awaiting release, and is attached to star in Jack and Diane opposite Ellen Page, with whom she co-starred in Juno.

Thirlby plans to attend college once she has made a sufficient start to her acting career.

Credit: Wikipedia