Born in New York City and raised in London, she began her career as a photography model, appearing in the pages of Italian Vogue and for the 2003 Pirelli Calendar.

She subsequently portrayed socialite Edie Sedgwick in Factory Girl (2006) and author Caitlin Macnamara in The Edge of Love (2008), and was nominated for the BAFTA Rising Star Award in 2008.

[10] With roles in two commercial films and a higher public profile due to her relationship with actor Jude Law, 2004 was a turning point for Miller's career.

The crime thriller Layer Cake, directed by Matthew Vaughn and starring Daniel Craig, featured her as the love interest of a London-based cocaine supplier.

The New York Times called Miller "a new It Girl who barely registers on-screen despite wearing little more than lacey filaments that make her look like a gift meant to be unwrapped very quickly".

[11] In Alfie, the remake of Bill Naughton's 1966 film, she played the girlfriend of a cockney limo driver and sex addict (Jude Law).

It made $37.6 million, and Entertainment Weekly, in a favorable review, wrote: "Ms. Miller has a modern, smart-girl look about her; her Francesca is neither too tough to melt nor too glittering from the Emma Thompson school of smarties".

Paul Taylor of The Independent wrote: "She approaches an emotion with the finesse of someone beating a carpet" and that she "brings to it all the ripe professional stage experience that can be mustered from appearing in three movies".

"[15] In 2007, Miller had a role as the love interest of a young man from a fictional British town in Matthew Vaughn's adaptation Stardust, and played a starlet in Steve Buscemi's Interview, a remake of Dutch filmmaker Theo van Gogh's 2003 movie of the same name.

[16] In The Mysteries of Pittsburgh (2008), a film adaptation of Michael Chabon's novel,[17] Miller played a woman romantically involved with a rebellious bisexual man.

"[19] Miller was parodied in Pittsburgh media (including one article headlined "Semi-famous actress dumps on the 'Burgh") and criticised for making what was seen as an unnecessarily disparaging remark, given the special treatment the film's cast and crew had received from the visitors' bureau and other city offices.

[20] In the 2008 British biographical drama The Edge of Love, Miller appeared alongside Keira Knightley as Caitlin Macnamara, the wife of poet Dylan Thomas.

[26] She appeared on the UK motorsport show Top Gear in 2009 on the segment "star in a reasonably priced car" and set a lap time of 1:49.8, having passed her driving test only five days before.

"[32] She starred as a former starlet caught up in a love-triangle in Trevor Nunn's 2011 production of Flare Path at London's Theatre Royal Haymarket.

[33] After her professional slump, Miller experienced what journalists called a "career revival"[29] She played more complex, dramatic parts in a series of critically acclaimed films.

[29] In The Girl (2012), an HBO and BBC film, Miller portrayed actress Tippi Hedren, the muse of director Alfred Hitchcock.

[36][37] The film received mixed reviews, but the Daily Mirror's Jane Simon wrote: "[G]liding gracefully through it all (and with an impeccable American accent) Sienna Miller brings untouchable beauty and icy glamour, but also captures the extraordinary resilience Hedren must have had to withstand everything Hitchcock threw at her."

In 2012, she also played a socialite in the dramedy Two Jacks, the hysterical sister of an elementary teacher in the drama Yellow, and a housewife who aspires to complete in a belly-dance competition in the made-for-television film Just like a Woman.

In 2014, Miller portrayed Nancy Schultz, the wife of murdered Olympic gold medal-winning wrestler Dave Schultz, in Bennett Miller's Foxcatcher, and Taya Renae Kyle, the wife of United States Navy SEAL sniper Chris Kyle, in Clint Eastwood's American Sniper.

[40] Miller also took the role of Sally Bowles in the Broadway revival of Cabaret after Emma Stone's scheduled departure from the production and performed for the last six weeks of the show's engagement, in February and March 2015.

The New York Daily News praised her "cocky and steely" performance and wrote that her approach to the role "works well in the Kander and Ebb songs 'Don't Tell Momma' and 'Perfectly Marvelous'.

[45] In Ben Affleck's period crime drama Live by Night (2016), Miller played the mistress of a notorious gangster and the love interest of a World War I veteran.

[46][47][48][49] In 2017, Miller starred in the drama The Private Life of a Modern Woman, which screened out of competition at the 74th Venice International Film Festival,[50] and in a West End production of the Tennessee Williams classic Cat On A Hot Tin Roof, at the Apollo Theatre.

[51] In 2018, Miller appeared in the war film The Catcher Was a Spy as Estella, the girlfriend of Moe Berg, a catcher for the Boston Red Sox who joined the OSS during World War II, as well as the drama American Woman, in which she portrays a single mother faced with raising her grandson after her daughter goes missing under mysterious circumstances.

The Guardian wrote that she was "vocally channelling Edie Falco from The Sopranos",[53] and with a worldwide gross of $50 million, the film was a moderate commercial success.

Miller struggled to find material on which to base her performance aside from the script and Gabriel Sherman's book The Loudest Voice in the Room.

[61] Miller appeared as a guest at a Rome retro-styled dinner party in Gucci's Cruise 2020 campaign, which was directed and photographed by American film director Harmony Korine.

[29] In a 2017 interview with The Sydney Morning Herald, she said: "I definitely feel like I'm in a place now where people are more focused on my career than on my private life and clothes, which is refreshing.

[95] Later, as a core participant, she gave evidence to the Leveson Inquiry in November 2011,[96] including the following:[97] I would often find myself almost daily, I was 21, at midnight running down a dark street on my own with 10 big men chasing me.

You've got a pack of men chasing a woman, and obviously that's a very intimidating situation to be in.In November 2021, Miller accepted a financial settlement from News Group Newspapers, publishers of The Sun, over an alleged phone hacking claim.