At the age of seven, Alexia Fast wrote, directed and starred in a short film entitled The Red Bridge. She starred in her first feature film, Fido, after gaining her first agent at the age of 11. She also appeared in television films such as His and Her Christmas, Past Tense and Firestorm: The Last Stand at Yellowstone. After she starred in Fido, she appeared in TV series until 2009, at which point she starred as Julie in the feature film Helen. Fast played a role in Hungry Hills and Repeaters, both of which premiered at the Toronto International Film Festival. In 2010, she had a leading role in Triple Dog. Shortly after, she shot her most recent episode of Supernatural and featured in Last Kind Words and Blackbird. In 2012, she had a supporting role in the film Jack Reacher.