Ahna O'Reilly (born Andrea Mariele Brewster O'Reilly, 21 September 1984, Palo Alto, California) is an American actress active since 2003. She graduated from Menlo School and attended the University of Southern California for one year before dropping out to pursue acting. Her breakthrough came in 2011 with the role of Elizabeth Leefolt in The Help, which earned the cast a SAG Award for Outstanding Performance by a Cast in a Motion Picture. She has also been recognized on stage, starring opposite Steven Pasquale in The Robber Bridegroom at Roundabout Theater Company, directed by Alex Timbers (a Lortel Award nominee for Outstanding Revival). She has received the 2014 ISTP Rising Star Award and is a philanthropist supporting Art of Elysium, UNICEF Next Generation, and Planned Parenthood. She is married to Dave Andron (m. 2020). Her filmography includes Forgetting Sarah Marshall (2008), Fruitvale Station (2013), Jobs (2013, as Chris-Ann Brennan), As I Lay Dying (2013), CBGB (2013, as Mary Harron), Get On Up (2014), She's Funny That Way (2015), All I See Is You (2017), Marshall (2017), Bombshell (2019, as Julie Roginsky), Our Friend (2019), and Where the Crawdads Sing (2022, as Ma). On television she has appeared in CSI: NY (2008), The Vampire Diaries (2011), How I Met Your Mother (2014), Kingdom (2017), The Morning Show (2019), Justified: City Primeval (2023), and Bodkin (2024, as Amber).
