McKnight began her career when she was seventeen in Disney Channel's TV Movie Go Figure. She then landed a supporting role in feature film Unaccompanied Minors in 2006. In 2007, she starred in the film Whisper Island, in which she played the role of Sam Dalton.
She is also known for her roles in the 2008 television series Lifeless and teen rom-com HottieBoombaLottie which was picked up by MTV.
In 2009 she played the lead role in MTV's My Super Psycho Sweet 16 as Skye Rotter. In 2010 she reprised her character Skye Rotter in My Super Psycho Sweet 16: Part 2. And for the final time in the 2012 third installment of the series, My Super Psycho Sweet 16: Part 3.
In 2013 McKnight played Elizabeth the "Lizard" on Once Upon a Time in Wonderland.
In January 2016 McKnight was the lead subject of a New York Times article about Los Angeles based actors and artists taking jobs driving for Uber and Lyft in between acting and artistic jobs.
