O'Reilly graduated from Menlo School in 2003 and attended the University of Southern California for one year before dropping out.

She has appeared in several other movies like Dinocroc, Nancy Drew, Just Add Water and Forgetting Sarah Marshall.

She also acted in television series like CSI: NY, Unhitched, The Vampire Diaries and Prime Suspect.

In 2011, she appeared in the movie The Help based on Kathryn Stockett's best-selling novel of the same name, a period piece set in Jackson, Mississippi, in the 1960s.

[8][9] In December 2021 O'Reilly announced via Instagram that she married writer and producer Dave Andron a year earlier, in secret.