Born in England, Guillory is the daughter of the American folk guitarist Isaac Guillory and his first wife, an English model. Her father was of Jewish heritage and born at the Guantanamo naval base in Cuba, the son of an American sailor and his Cuban-Turkish wife.
Her parents moved to Fulham, London when Guillory was two, then later to Norfolk when she was eleven. At the age of ten, she went to stay with cousins in Mexico to learn Spanish. She has a half-brother, whom her father had adopted and with whom she shares the same mother. Her parents divorced in 1990 when she was fourteen, and in 1993 her father remarried, which resulted in a much younger half-sister and half-brother. Guillory attended Gresham's School in Holt, Norfolk, where she took part in numerous school productions. She was later expelled from the school for stealing.
Guillory has been an equestrian since the age of two. At fourteen, she was given a horse, which she named The Night Porter, or Porty, after the film The Night Porter; Guillory was a fan of its leading actress Charlotte Rampling. She still often rides horses with her mother.
Before becoming a model to support her acting career, Guillory waited tables at a club. In 1997, Guillory accompanied a ballerina friend to the London modeling agency Select and was soon signed. As a model, she worked in campaigns for Armani, Dolce & Gabbana, Burberry and Paul Smith and appeared on the covers of British, German and Italian Vogue, among other fashion magazines. In 1999, she became the face of the Hugo Boss fragrance campaign and continuing the campaign for three years. After modeling for a few years, Guillory returned her focus to acting in 2000.
During her time as a model, she studied acting at the New World School of the Arts and the Paris Conservatoire, also taking small television and film roles in The Future Lasts a Long Time (1996), The Rules of Engagement (1999), Star! Star! (1999), Kiss Kiss (Bang Bang) (2000), The 3 Kings (2000), and Two Days, Nine Lives (2000).
After deciding to focus her career on acting, she returned to film with a more substantial role in the thriller Sorted (2000). Guillory went on to appear in the BBC production Take a Girl Like You, a television adaptation of Kingsley Amis's novel of the same name. She portrayed Jenny Bunn, the story's virginal heroine, and gained critical attention for her part in the period piece.
2002 saw Guillory appear in The Time Machine, alongside Guy Pearce and Jeremy Irons. She played Emma, the fiancée of Pearce's character, who was killed early in the film and whose death set off its main events.
Guillory had a small role in the romantic comedy Love, Actually before taking the starring role in the television miniseries Helen of Troy. The series was mostly based on Homer's epic poem Iliad and focuses on the mythological life of Helen. Helen of Troy was nominated for best miniseries at the Satellite Awards.
In May 2004, Guillory starred in a new stage production of The Shape of Things at the New Ambassadors Theatre in London. 2004 also saw Guillory in her first big Hollywood role. She was cast as Jill Valentine, one of the lead characters in the video game adaptation sequel Resident Evil: Apocalypse.
In 2006, Guillory was a lead in the ensemble cast of the fantasy Eragon, the film adaptation of the novel by Christopher Paolini; she portrayed Arya Dröttningu, an elf princess. The film was not well received by the critics, but was nominated as Best Fantasy Film at the 2006 Saturn Awards.
In 2007, she starred in the Spanish production El Corazón de la Tierra, or The Heart of the Earth, and later in the year finished filming the horror/thriller Victims and the fantasy novel adaptation Inkheart where Guillory acted alongside Helen Mirren, a friend of the Guillory family who was a role model when she first had aspirations towards acting.
- The Big Bang (2010) - Julie Kestral
- Gunless (2010) - Jane
- Perfect Life (2010) - Anne
- Virtuality (2009) - Rika Goddard
- Inkheart (2008) - Resa
- The Oaks - Pilot (2008) TV episode - Jessica
- Criminal Minds - Lo-Fi and Mayhem (2008) TV episodes - Kate Joyner
- El Corazón de la Tierra (2007) - Katherine
- Eragon (2006) - Arya
- Eragon (2006) (VG) (voice) - Arya
- Rabbit Fever (2006) - Newscaster
- The Virgin Queen - 4 episodes (2006) TV episodes - Lettice Knollys
- Silence Becomes You (2005) - Grace
- In the Bathroom (2005) - The woman
- Marple: A Murder Is Announced (2005) - Julia Simmons
- Beauty (2004) - Cathy Wardle
- Resident Evil: Apocalypse (2004) - Jill Valentine
- Love Actually (2003) - Jamie's Girlfriend
- Helen of Troy (2003) - Helen
- The Principles of Lust (2003) - Juliette
- The Time Machine (2002) - Emma
- Superstition (2001) - Julie
- The Last Minute (2001) - Kayak Girl
- Two Days, Nine Lives (2001) - Kate
- Late Night Shopping (2001) - Susie
- Oblivious (2001) - Jessica
- Take a Girl Like You (2000) - Jenny Bunn
- Sorted (2000) - Sunny
- The 3 Kings (2000) - Roxana
- Kiss Kiss (Bang Bang) (2000) - Kat
- Star! Star! (1999) - Lu
- Dzvirpaso M (1999)
- The Rules of Engagement (1999) - Denise
- Out of Sight - Getting Rid of Ingrid and Close Encounter (1996) TV episodes - Ingrid
- The Future Lasts a Long Time (1996) - Blue
- The Buccaneers - 5 episodes (1995) TV episodes - Lady Felicia Marabel
- Riders (1993) - Fenella Maxwell
- For an up-to-date Filmography: imdb.com/Sienna Guillory
- In 1995, a few years after separating from Guillory's father, her mother, established her own business, The Carrier Company, designing and making country clothes, which she still runs from a 17th century farmhouse at Wighton in Norfolk.
- In December 2000, Guillory's father died of cancer at the age of fifty-three. When diagnosed, doctors told him he had had the cancer for six years. About her father's health, she has explained that the cancer was supposedly brought on when Isaac was performing in Wales shortly after the nuclear incident at Chernobyl. After his show, Isaac Guillory wore a jacket soaked in rain from the Welsh location for a five-hour drive. He learned afterwards that the rain contained fallout from the incident. Isaac's cancer was on his back and shoulders, the reason why he believed the rain had caused it.
- She is interested in homoeopathy and natural remedies, saying that when she was a child her mother worked at a health food shop and was hesitant to give antibiotics. Guillory is also a fan of acupuncture.
- In August 2004, Guillory and Cilenti cycled five stages of the Tour de France to raise money for charity. Guillory supports Amnesty International and Shelter.