Sienna Rose Miller was born in New York City, on December 28, 1981. She is the daughter of Edward Miller, an American banker, and Jo Miller, a South-African who ran Lee Strasberg's acting academy in London. Culturally, she considers herself English.

For much of her childhood and adolescence, her stepmother was the English interior decorator Kelly Hoppen. She has one sister, Savannah; two half-brothers, Charles and Steven; and one former step-sister, Natasha (daughter of Kelly Hoppen).

Sienna went to a boarding school in Ascot, Surrey and developed a passion for film as well as training as a singer, and doing a bit of modeling. After school she moved back to New York to study acting full time at the Lee Strasberg Institute and appeared in a few NY productions. Sienna secured a top UK agency to hunt down roles for her and she appeared in the BBC series Bedtime. This led on to 'Keen Eddie', and she has reportedly signed a seven-year film deal with Paramount Pictures! While in the UK, Sienna lives in Notting Hill.

The actress performed in numerous NYC productions, including “A School for Scandal” by British playwright Richard Brinsely Sheridan and “Cigarettes and Chocolate” by writer/director Anthony Minghella. Miller made the jump to television with her role as Fiona Bickerton on “Keen Eddie”, where she played a British woman forced to live with an NYPD detective (Valley), who is on the trail of a drug dealer he let get away back in the States.

Miller was also cast in a remake of the 1966 comedy classic, “Alfie” (2004). In the update, Miller played one of many women seduced by the roguish Cockney, Alfie (Law) who appears at first to be his perfect, undemanding match--and indeed, the actress' edgy performance was singled out as one of the remake's finer elements. Miller and Law spent most of the shoot avoiding the paparazzi, who smelt a story once they realized the two stars were together, despite Law being in the midst of divorce proceedings with actress Sadie Frost. Before the ink was dry on the papers, Law moved into an NYC apartment with Miller to allow their romance to “blossom away from prying eyes."

Her skills as an actress attracted the attention of British producer Matthew Vaughn of “Lock, Stock and Two Smoking Barrels” (1999) and “Snatch” (2001) fame. Vaughn cast Miller in his first feature as director, “Layer Cake” (2004), another British gangster comedy involving thugs, drugs and double crosses. In 2005 while Miller was appearing in London's West End production of "As You Like It " her fiancé Law made a public admission of infidelity, apologizing for an affair with his children's nanny (a teary-eyed Miller appeared in the play the day the news broke, but was subsequently replaced by her understudy). The couple's seemingly on-again, off-again relationship captivated the press for several months in 2005; meanwhile, she demonstrated her continuing growth as an actress in "Casanova" (2005), director Lasse Hallstrom's fictionalized account of the legendary lothario (Heath Ledger) falling in love at last, was easily one of the most ill-conceived and disappointing films of the year, despite lavish production values and game performances by Miller--playing the strong-willed, independent-minded Italian noblewoman and secret author who captures Casanova's heart-- and the rest of the all-star cast.