Schilling was born in Boston, Massachusetts, the daughter of Patricia (née Miller), an MIT administrator, and Robert J. Schilling, a former prosecutor. She grew up in West Roxbury and Wayland, splitting time between her divorced parents. A fan of the NBC medical drama ER during her youth, she began acting at a young age. She became active in her middle school's theater program when she appeared in a stage production of Fiddler on the Roof.
After graduating from Wayland High School in 2002, Schilling attended Fordham University's campus at Lincoln Center, where she continued to take part in stage productions before earning her Bachelor of Arts in 2006. She then entered the graduate program at New York University to continue her acting studies, but left after her second year to start auditioning. While she attempted to break into acting, she supported herself by working as a nanny for a Manhattan-based family.
Schilling made her feature film debut with a supporting role in the independent filmDark Matter (2007). In 2009, she was selected to star in the NBC medical drama Mercy, as Nurse Veronica Flanagan Callahan, a tough Iraq War veteran and former military nurse-turned-medical practitioner. Reading for the part via videotape from New York City, she impressed the show's creator and executive producer, Liz Heldens, who then flew her out to Los Angeles to audition for the role. In Heldens' words, "she just blew the doors off the audition." The show ran for one season from September 2009 to May 2010.