O'Reilly graduated from Menlo School in 2003 and attended the University of Southern California for one year before dropping out. She dated actor James Franco for a time before the two broke up in 2011.
In 2016, she appeared in the Roundabout Theatre Company off-Broadway production of The Robber Bridegroom. A cast recording featuring O'Reilly in her role as Rosamund was released on September 9, 2016.
