Sienna Miller was born in New York, educated in England, and studied drama at the Lee Strasberg Institute. Her film debut came in 2004 opposite Daniel Craig in Layer Cake. From there, she appeared in Factory Girl, Casanova, The Edge of Love, Interview and GI Joe: The Rise of Cobra. Miller received a British Independent Film Award nomination for Best Supporting Actress for her role in The Edge of Love, and both a BAFTA Orange Rising Star Award and an Independent Spirit Award for her performance in Interview. In 2013, she was nominated for a BAFTA TV and a Golden Globe for her role in HBO's The Girl playing Alfred Hitchcock's muse Tippi Hedren.

In 2015, Miller starred in Foxcatcher, nominated for five Academy Awards. In the same year, she starred opposite Bradley Cooper in Clint Eastwood's Academy Award Best Picture nominee American Sniper. Other film credits include Unfinished Business, Burnt, and her British Independent Film Award-nominated role in High-Rise. Miller also played the enthralling Emma Gould in Live By Night and the early feminist Nina Fawcett in The Lost City of Z directed by James Gray.

In 2019 Miller played Deb in American Woman, directed by Jake Scott, with co-stars Aaron Paul and Christina Hendricks. Her performance received outstanding reviews from the LA Times, TheWrap, Vogue among others. Two other 2109 projects were Showtime's The Loudest Voice, playing Elizabeth Ailes, wife of Roger Ailes (played by Russell Crowe), and 21 Bridges with Chadwick Boseman and J.K. Simmons.

Stage credits include the Broadway productions of Cabaret and After Miss Julie, and Flare Path, As You Like It, and Cat on a Hot Tin Roofin London's West End. Outside of her acting career, Sienna serves as Global Ambassador for the International Medical Corps.