The five-part series has been penned by author Anthony Horowitz, who recently worked on Collision.
Purefoy will star in the show as William Travers, a criminal barrister who is recovering from a series of traumatic events which have made him question the legal system.
He eventually becomes involved in a case surrounding his old friend Martin Newall (Nathaniel Parker) who is facing conspiracy and murder charges while being investigated by vengeful detective DS Mark Wenborn (Creed Miles).
The series is described as a story of "friendship, conspiracy, betrayal and murder" and is said to take a critical look at the legal system.
ITV's director of drama commissioning Laura Mackie said: "Anthony is such a talented screenwriter and the quality of his scripts has attracted top flight acting talent. We're totally committed to original, authored drama and this commission is a brilliant addition to our slate for 2011."
Meanwhile, Horowitz said: "Laura Mackie asked me to come up with a psychological thriller that would keep audiences guessing to the end and I hope with Injustice I've done just that."
Filming for Injustice has begun and will continue for ten weeks in Suffolk and London.