Robertson's early career saw her performing on stage at the Greenville Little Theater, before transitioning to screen, making her debut in an episode of Sheena in 2000.

Her subsequent roles in television and film, included Power Rangers Time Force, The Ghost Club, and more significant parts in Growing Pains: Return of the Seavers, Dan in Real Life, and The Tenth Circle.

Robertson gained wider acclaim for her performances in Under the Dome (2013–2014), Tomorrowland (2015), and as the lead in Girlboss (2017), portraying a fictionalized version of entrepreneur Sophia Amoruso.

Robertson appeared in CSI: Crime Scene Investigation in the episode "Go to Hell", and had a role as a recurring character in the CBS television series Swingtown.

She also made a guest appearance on Law & Order: Special Victims Unit in the episode "Babes" as Tina Bernardi, a Catholic teen who gets pregnant in a pact.

Robertson played the lead role of Lux Cassidy in the television drama series Life Unexpected (2010–2011), which was cancelled in its second season despite positive reviews.

That same year, she headlined the Netflix comedy television series Girlboss, portraying a fictionalized version of self-made millionaire Sophia Amoruso.

In April 2019, Robertson was cast in the role of Melissa Henning, the real-life wife of Christian rock musician Jeremy Camp, in Lionsgate's faith-based biographical romance film I Still Believe.

In January 2021, Robertson was added to the cast of the ABC drama Big Sky as recurring character Cheyenne Kleinsasser.