Szostak is half-French and half-American, and was raised in the suburbs of Paris, France. She moved to the United States to study business at The College of William & Mary in Williamsburg, Virginia. After graduating, she moved to New York and worked for Chanel in marketing but soon realized she was in the wrong profession and switched to acting after taking some classes. New York Times movie critic Stephen Holden described her as a "smoldering star" when he saw her performance in the 2006 film Satellite.
Szostak, her Polish married name, is pronounced "Show-stack".
