Following a minor role as Sabé in Star Wars: Episode I – The Phantom Menace (1999), her breakthrough came when she played a tomboy footballer in Bend It Like Beckham (2002) and co-starred in Love Actually (2003).

She took on contemporary-set parts in Begin Again (2013) and Jack Ryan: Shadow Recruit (2014), and returned to historical films playing Joan Clarke in The Imitation Game (2014), earning a nomination for the Academy Award for Best Supporting Actress.

Knightley's parents encountered substantial financial difficulties following the birth of her brother;[6] her father, a "middling" actor, agreed to a second child only if her mother sold a script first.

After appearing in a spate of television films through the mid-to-late 1990s, including Innocent Lies (1995), The Treasure Seekers (1996), Coming Home (1998), and Oliver Twist (1999),[16] Knightley landed the role of Sabé, Padmé Amidala's handmaiden and decoy, in the 1999 science fiction blockbuster Star Wars: Episode I – The Phantom Menace.

Knightley was initially sceptical of the project: in an interview with Tracy Smith she said, "I remember telling friends I was doing this girls' soccer movie [...] And nobody thought that it was gonna be any good.

[29] The film, based on the Disney theme park attraction, revolves around infamous buccaneer Jack Sparrow and blacksmith Will Turner rescuing Swann, in possession of a cursed golden medallion, from 18th-century pirates.

[36][37] Also in 2003, Knightley appeared in Richard Curtis's Christmas-themed romantic comedy Love Actually, featuring an ensemble cast, which included her childhood idol Emma Thompson.

[49] In a mixed review for Empire, Kim Newman wrote that the role was unlike the ones she had previously taken up : "getting out of period gear and talking American, tries to broaden her range and is arguably well-cast".

[55] Writing for The Guardian, Peter Bradshaw labelled her performance of "beauty, delicacy, spirit and wit; in her growing lustre and confidence" and Derek Elley of Variety found her "luminous strength" to be reminiscent of a young Audrey Hepburn.

[60] In 2004, the second and third films of the Pirates of the Caribbean series were conceived, with screenwriters Ted Elliott and Terry Rossio developing a story arc that would span both sequels, in which Knightley reprised her role as Elizabeth Swann.

The plot of the films see Swann buck convention to seek adventure and become fierce pirate and fighter to match the skills of Sparrow and her love interest, Turner.

[31] Filming for the projects took place in 2005; Pirates of the Caribbean: Dead Man's Chest released in July 2006, with the worldwide collections of $1.066 billion, becoming the biggest financial hit of Knightley's career.

[66][67][68] Knightley's continued association with period dramas yielded varying results, as seen with two of her 2007 releases, François Girard's Silk, and Joe Wright's Atonement, the feature film adaptations of the novels by Alessandro Baricco and Ian McEwan respectively.

[77][78][79] Knightley appeared alongside Sienna Miller, Cillian Murphy, and Matthew Rhys in John Maybury's 2008 wartime drama The Edge of Love.

[90] Knightley chose the role as she felt that "if I don't do theatre right now, I think I'm going to start being too terrified to do it" and described the production as an "extraordinary and incredibly fulfilling" experience, she was sceptical of her performance.

[101] Knightley's sole film release of 2011 was David Cronenberg's historical drama A Dangerous Method, co-starring Viggo Mortensen, Michael Fassbender, and Vincent Cassel.

Based on writer Christopher Hampton's 2002 stage play The Talking Cure and set on the eve of World War I, the film depicts the turbulent relationships between fledgling psychiatrist Carl Jung, his mentor Sigmund Freud and Sabina Spielrein.

[117] Later that year, she appeared in Karl Lagerfeld's short period film Once Upon a Time ...[118] In July 2014, Knightley stated that she had reached the end of the first stage of her career, and wished to depart from "neurotic" roles.

[122] A romantic comedy also starring Chloë Grace Moretz and Sam Rockwell, the film follows the life of Megan, played by Knightley, a 28-year-old overeducated underachiever going through a quarter-life crisis.

Knightley portrayed cryptanalyst and numismatist Joan Clarke, who decrypted German intelligence codes for the British government during World War II with Turing.

[132] In October 2015, Knightley made her Broadway debut playing the title role in Helen Edmundson's adaptation of Émile Zola's Thérèse Raquin at Studio 54.

[134] Of her performance, Alexandra Villarreal of The Huffington Post wrote: "She fumes, and rages, and withdraws, and you can watch her psychological evolution from stifled wife to impassioned mistress to haunted murderer".

[143] Manohla Dargis of The New York Times praised her vibrance and "expressive physicality", and Jordan Hoffman of The Guardian wrote that the film saw Knightley in "top form: luminous, clever, sexy and sympathetic.

[163] Knightley was due to produce and star in The Essex Serpent, an Apple TV+ adaptation of Sarah Perry's novel,[164] but dropped out over concerns about access to childcare during the lockdown period of the COVID-19 pandemic.

[173] Writing for The New York Times, Jesse McKinley stated that Knightley is "known for her ability to sparkle and charm in several accents", while her Thérèse Raquin co-star, Judith Light, praised her "down-to-earth demeanor, intelligence and sense of humor".

[181] Writer Anne Helen Petersen states that the varying personalities of her historical roles are united in the "larger idea" Knightley represents: "that of women ostensibly performing a version of proper womanhood — all while quietly negotiating, or cracking under, the weight of doing so.

[192] Knightley posed topless for the September 2014 cover of Interview magazine, on condition that the image not be digitally altered, to draw attention to how "women's bodies are a battleground and photography is partly to blame.

The video, titled "What They Took With Them", has the actors reading a poem, written by Jenifer Toksvig and inspired by primary accounts of refugees, and is part of UNHCR's #WithRefugees campaign, of which also includes a petition to governments to expand asylum to provide further shelter, integrating job opportunities, and education.

She recounted how she did not leave her home for three months up until early 2008, and needed to have hypnotherapy to prevent panic attacks so she could be able to attend that year's BAFTA Awards, where she was nominated for her performance in Atonement.

[234] According to the review aggregator site Rotten Tomatoes, Knightley's most critically successful films are Bend It Like Beckham (2002), Love Actually, (2003), Pirates of the Caribbean: The Curse of the Black Pearl (2003), Pride & Prejudice (2005), Atonement (2007), The Duchess (2008), Never Let Me Go (2010), A Dangerous Method (2011), The Imitation Game (2014), Everest (2015), Colette (2018), Official Secrets (2019), and Misbehaviour (2020).