Collins began acting at the age of two in the BBC series Growing Pains. She was a guest star on 90210 in 2009, followed by her feature film debut in the semi-biographical sports film The Blind Side. She was named One to Watch by the Young Hollywood Awards for her roles in the sci-fi action-horror film Priest (2011) and the psychological action-thriller film Abduction. She was nominated for the Teen Choice Award for Choice Movie Actress – Sci-Fi/Fantasy for her role as Snow White in the fantasy film Mirror Mirror and for the Teen Choice Award for Choice Movie Actress – Action for portraying Clary Fray in the fantasy film The Mortal Instruments: City of Bones. Collins is also known for her roles in the films Stuck in Love (2012), The English Teacher (2013), and Love, Rosie (2014). Lily can currently be seen playing the role of Cecelia Brady in the Amazon TV series The Last Tycoon.