Cross was born in New Brunswick, New Jersey to Maureen and Michael Cross. He has four siblings, Liz, Brian, James and Andrew and had what he has described as a "pretty normal" upbringing. His brothers Andrew and James currently attend Pelham Middle School, in Pelham New York.

As a child actor, Cross appeared in the Hollywood films Desperate Measures, M. Night Shyamalan's Wide Awake and Jack Frost, all of which were released in 1998. Throughout the late 1990s and early 2000s, he also appeared in several television roles.

In 2006, Cross played Augusten Burroughs in Running with Scissors, a drama also featuring Annette Bening and Evan Rachel Wood, and appeared as real-life soldier Franklin Sousley in the big-budget Flags of Our Fathers, a Clint Eastwood-directed war film. Cross has said that he enjoyed the transition from appearing in Running with Scissors, which he has described as "very character driven and smaller" to the high-profile "epic" Flags of our Fathers. Running with Scissors has been described by media sources as Cross's "breakout performance". Cross's next film will be Untraceable, in which he will play an online predator tracked by an FBI agent (Diane Lane).

Cross attends Trinity College, a private liberal arts college in Hartford, Connecticut.