Cuthbert was born in Calgary, Alberta, the daughter of Patricia, a homemaker, and Kevin, an automotive design engineer. She has two younger siblings, Jonathan and Lee-Ann, and she grew up in Greenfield Park, near Montreal, Quebec.
Fox played Lindsay Lohan's rude nemesis in Confessions of a Teenage Drama Queen (2004), then earned praise for her comic sensibilities on the TV sitcom Hope & Faith (Fox replaced actress Nicole Paggi in the second season and was on the show from 2004-06)