Tunney exposed acting at a Chicago Academy for the Performing Arts. She moved to Los Angeles, at the age of Eighteen, in which she got many recurring TV roles in Law & Order, Dream On, and Life Goes On. She experienced the major breakthrough by having her role as a self-destructive adolescent within Empire Records before receiving a leading role as a gothic witch in The Craft, alongside Fairuza Balk, Neve Campbell and Rachel True.

Tunney besides starred paired Arnold Schwarzenegger in the 1999 action film End of Days. She presently stars in Prison Break.

Around 1997, Tunney married producer Bob Gosse.

Tunney occurs as South Side Chicago native. She went to St. Ignatius College Prep, a coed Catholic high school in Chicago.

Select filmography
Empire Records 1995 The Craft 1996 Julian Po 1997 End of Days 1999 Cherish 2002 Prison Break (TV series) 2005 Runaway 2005