Born and raised in Bangor, Maine, Niznik began her acting career in the theatre in such productions as Crimes of the Heart and Dial M for Murder. She made the transition to television with guest-starring appearances on such hit shows as Dr. Quinn, Medicine Woman, Profiler, JAG, Frasier, Diagnosis Murder and eventually becoming a series regular on Guardian Angel and Vanishing Son.
Niznik's previous film credits include Kismet, Memorial Day, Star Trek IX and Garry Marshall's Dear God.
She received her Masters of Fine Arts from Duke University in North Carolina.