O'Brien is signed with Ford Models. She started at the age of five when her mother got her into television commercials, and subsequently got into modeling at the age of 13. During her teenage years she modeled for the likes of Guess and Pottery Barn. O'Brien appeared in the Girlfriend perfume campaign with Justin Bieber, and as an extra in his music video, "One Time". She began her acting career in 2012, when she guest starred in an episode of Jessie playing the role of Diamond Bloodworth.
In 2014, she joined the cast of the Daytime Emmy Award winning soap opera Days of Our Lives, portraying the role of Paige Larson; she debuted on March 3, 2014. O'Brien is signed to a two-year deal with the series. In June 2015, it was reported that O'Brien was let go from the soap, and last appeared on September 9, 2015. In 2016, she joined the upcoming series Queen Sugar as Stella.
O'Brien has been dating her former Days of Our Lives co-star Casey Moss since 2015.
