Ahna O'Reilly is an American actress born on September 21, 1984, in Palo Alto, California. She grew up in a creative family, with her father, James O'Reilly, being a travel writer and her mother, Wenda O'Reilly, creating educational games for children. She  has two sisters, Noelle and Mariele. She attended Menlo School and later enrolled at the University of Southern California, though she left after a year to pursue her passion for acting.

She began her acting career in 2003 with the film "Bill the Intern." Over the years, she appeared in various movies and television shows, gaining recognition for her talent and versatility. One of her most notable roles was in the 2011 film "The Help," where she played Elizabeth Leefolt. 

The movie, based on Kathryn Stockett's novel, was a critical and commercial success, earning several ensemble awards, including the Screen Actors Guild Award for Outstanding Performance by a Cast in a Motion Picture. 

She also appeared in films like "Jobs," "Fruitvale Station," and "Where the Crawdads Sing," showcasing her ability to take on diverse roles. Her television credits include appearances in popular series such as "CSI: NY," "The Vampire Diaries," and "The Morning Show."

In her personal life, she was previously in a relationship with actor James Franco, which ended in 2011. In December 2021, she revealed that she had secretly married writer and producer Dave Andron a year earlier. She is known for her grounded and private lifestyle, balancing her professional commitments with her personal life. 

Throughout her career, she has received recognition for her work. Her performance in "The Help" earned her and the ensemble cast several awards, including the National Board of Review Award and the Hollywood Film Award for Ensemble of the Year.