Smart was born in Birmingham, England. Her career started as a child, notably in the television series Woof! She is best known for a series of well-regarded television roles including Virginia Braithwaite, daughter of a lottery winning family in the comedy drama At Home with the Braithwaites. Sparkhouse (Red Production Company / BBC 2002); and her appearance in Jane Hall (Red Production Company / ITV1 2006) marked a fruitful link between Smart and television writer Sally Wainwright. Between 2008 and 2010, she was featured as Anne-Britt Hoglund in Wallander, six feature-length adaptations of Henning Mankell's Wallander novels, for the BBC. Smart has also been featured successfully on radio.
She was a pupil of St Paul's School For Girls in Birmingham and has since returned during summer fetes to sign autographs.