Lily Collins was previously a fan of the books. When she found out that a film was being made, she made numerous phone calls to ensure her role as Clary.
Actor Matthew Daddario originally auditioned for the role of Alec Lightwood, but lost to Kevin Zegers. Daddario was later cast as Alec in the TV adaptation Shadowhunters: The Mortal Instruments (2016).
When Clary comes home to find her mother asleep, the background music is the song Jace shows Clary on the piano.
In real life, Lily Collins and Jamie Campbell Bower dated in 2013 but broke up before the movie was released. In 2015, they came back together, but broke up soon after.
Alex Pettyfer was first choice for the role of Jace Wayland, but turned it down. Alexander Ludwig, Xavier Samuel, Nico Tortorella, Leebo Freeman, Max Irons, Ed Speleers, Douglas Booth and Lucas Till, all auditioned for the role but lost to Jamie Campbell Bower