O'Reilly came across a "Models Wanted" link while viewing pornography. She filled out the application and was contacted three days later to shoot her first three scenes. Her adult film career began in August 2011 for Mofos in Miami, Florida. She stars in the role of Dorothy Gale in the 2013 pornographic film Wizard of Oz XXX. She was placed on CNBC's list of "The Dirty Dozen: Porn's Most Popular Stars" in 2014.
In 2014, O'Reilly made her directorial debut with Maddy O'Reilly is Slutwoman, which she co-directed alongside MimeFreak. The first film she directed on her own was Maddy O'Reilly's Submission, which won the 2015 XBIZ Award for BDSM Release of the Year.
In August 2015, O'Reilly appeared in an episode of the Lifetime television series Living with the Enemy to defend her career against a self-proclaimed anti-pornography life coach.
