Sienna was born on December 28, 1981 in New York, USA to Edward Miller and Jo Miller. Her father is an American banker, while mother is a South African who ran Lee Strasberg's acting academy in London. Her stepmother Kelly Hoppen is an English interior decorator. Sienna has one sister, Savannah, two half-brothers, Steven and Charles and one former stepsister, Natasha daughter of Kelly Hoppen. Although she is born in USA, she moved to England in her childhood and raised there. Sienna culturally considers herself as English.
Sienna Miller received her primary education at the all girl boarding school Heathfield School in Ascot, Surrey. Sienna enjoyed her school life very much like often snuck off to buy alcohol, pulled pranks, later studied full time at New York's Lee Strasberg Institute and excelled in acting.
Miller performed in many NYC productions like "A School for Scandal", "Cigarettes and Chocolate", "The Striker", and "Independence".
Sienna modeling career get started when she was spotted by Tandy Anderson, the owner of the Select Model Management agency. She was offered the chance of modeling and she signed immediately. Later she retuned back to UK and started there working as a model. Sienna has done shot for European commercials for Coca-Cola and also worked for Italian Vogue and Prada. Also modeled for 2003 Pirelli Calendar.
In 2002, Sienna was signed on by the PFD talent agency, who gave her a part in the independent feature "High Speed". In which she played a role of girlfriend torn between two best friends. The same year she appeared in a guest-starring role on FOX's series "The American Embassy". Also appeared in the 2002 season of the offbeat BBC miniseries "Bedtime".
As slowly she was getting the attention of people, Paramount Pictures signed her up to a seven-year contract. According to that deal her first job was the co-starring role as Fiona Bickerton on FOX's 2003 series "Keen Eddie", directed by Simon West.
In 2004, Sienna was found in supporting roles in the London crime drama "Layer Cake" and the remake of 1966 movie "Alfie" with Jude Law and Marisa Tomei. In 2005, she appeared in lead role opposite Heath Ledger in period drama, "Casanova". Sienna made a London's West End debut as Celia in Shakespeare's "As You Like It".
Sienna's upcoming projects include "Factory Girl" it is the highly anticipated bio-pic of 1960s socialite, while Sienna is playing the role of Andy Warhol's muse Edie Sedgwick. Factory Girl is going to release in September 2006. "Camille" is also due out in 2006. Her 2007 project are "Stardust" and "Interview". Currently Sienna is modeling for Pepe Jeans and also posed for Vanity Fair magazine's 2006 Hollywood Issue.
Rumors are floating around that, Sienna Miller is currently dating Hayden Christensen her co-star "Factory Girl". Sienna Miller was dated Jude Law from December 25, 2004 to July 2005, but later reestablished there relationship. Also dated model David Neville from 2001-2003, before that she was dated briefly to actor Orlando Bloom in 2001.