Cox, a St. Croix native, moved with her family to Orlando, Florida at age seven after spending five years of her youth studying dance in the U.S. Virgin Islands. In 1989, Cox was invited to participate in the Disney's Magic Kingdom Christmas Spectacular show. Due to her proximity to Universal Studios, Cox was able to earn roles as a child actor in various Nickelodeon shows such as My Brother and Me, Keenan and Kel, and All That.

Cox was a 1999 graduate of Dr. Phillips High School where she was enrolled in the Visual and Performing Arts magnet program for vocal performance. Cox earned a Bachelor of Music degree from Florida State University in 2003 after being accepted to their Musical Theater program. During her summers she worked at the Heritage Repertory Theater in Charlottesville, Virginia where she played roles in Smokey Joe's Cafe and Anything Goes one summer and performed as a recurring character in Nickelodeon's show Noah Knows Best during another. Other regional theater credits include Rent in which she played club Dancer and drug addict Mimi Márquez, the Chicago role of Liz, and Frenchie in Cabaret.

Prior to her role on Undercovers Cox made guest appearances on several television shows. In 2005, she appeared in CSI: NY, and Half & Half, and she appeared in One Tree Hill as Faith in season 3 episode 10 the following year. She also has a role in the marital crisis comedy Crazy, Stupid, Love., which was released in July 2011.

On October 29, 2009, she was one of the This is It Dancers who appeared on The Ellen DeGeneres Show to fulfill host Ellen DeGeneres' birthday wish.

She appeared in all first-season episodes of Undercovers. She plays a character named Lizzy Gilliam, who is the sister of the female lead and who is unaware of her family's involvement in Central Intelligence Agency activities. Originally, Jessica Parker Kennedy was cast in the role, but Cox replaced her in June 2010 before the first episode of the first season was aired in September 2010. Her character is described as "Boy crazy". Cox says that Lizzy's character, which spends much of her onscreen time running the family catering Business, embodied much of her own true character and described the character as follows: "Lizzy's a good character; very light-hearted, very fun loving, she’s got a good heart and an interesting past and she’s trying to deal with it".

In 2016, Cox appeared in the Modern Family episode "The Cover-Up" . On August 23, 2016, Cox joined Chicago Med in a recurring role. She portrays Tiana in the seventh season of Once Upon a Time. In August 2017, Cox was promoted to a series regular on the series.