Samantha Jane Morton was born in the Clifton area of Nottingham on 13 May 1977, the third child of Pamela (née Mallek), a factory worker, and Peter Morton. She is of Polish/Irish descent. She has six half-siblings from her parents’ relationships subsequent to their 1979 divorce. She lived with her father until she was eight, when she was made a ward of court because neither of her parents could care for her and her siblings. Her father was an abusive alcoholic, and her mother was involved in a violent relationship with her second husband; as a result, she never lived with her parents again.

After joining Central Junior Television Workshop at the age of 13, she was soon being offered small-screen roles such as Clare Anderson in the first series of Lucy Gannon’s Soldier Soldier and also Mandy, in an episode of Boon —both were ITV Central productions. Moving to London at sixteen, Morton applied to numerous drama schools, including RADA, without success. In 1991, she attended Clarendon College of Performing Arts to gain a BTEC award but subsequently left for personal reasons. She made her stage début at the Royal Court Theatre, and continued her television career with appearances in Peak Practice and in an episode of Cracker. At the time, she had a regular role in the first two series of Kay Mellor’s successful Band of Gold (1995–96).

Impressed by her performance in Under the Skin, Woody Allen cast her in Sweet and Lowdown, a romantic comedy about a fictional jazz guitarist in the 1930s (played by Sean Penn) who regards himself as the second greatest guitarist in the world. Morton played Hattie, a mute laundress and the love interest of Penn’s character. The film was released in September 1999, to wide critical acclaim and moderate success at the box office in the arthouse circuit. George Perry for BBC.com found her to be “extraordinary” as an “adoring mute who suffers […] She uses her eyes to convey meaning, reviving techniques of silent cinema”. Morton earned Academy Award and Golden Globe nominations for Best Supporting Actress for her role, which was especially notable, considering the fact that she does not utter a single word of dialogue in the film. During a 2007 interview with UK’s The Guardian, she remarked that her Oscar nomination meant “incredible things for me in the [United States]. I’m grateful for that. It means that […] I’m able to support the industry”.

Morton would next star in the small scale drama Jesus’ Son, which found a limited release, and praise from critics. She received a Satellite Award nomination for Best Supporting Actress – Motion Picture for her performance. Her other film in 1999 was the romantic drama Dreaming of Joseph Lees, an adaptation of a story written by Catherine Linstrum set in rural England in the late 1950s; for her part, she won the Evening Standard British Film Award for Best Actress. She appeared in the biographical drama Pandaemonium (2000), directed by Julien Temple, playing Sara Coleridge, the wife of the poet Samuel Taylor Coleridge. She was nominated for a British Independent Film Award in the category of Best Actress. Morton also played a mermaid opposite Larry Mullen in the Anton Corbijn-directed promotional video for U2’s “Electrical Storm”, and provided the voice of Ruby for the Canadian animated series Max & Ruby from 2002 to 2003.

Morton dated actor Charlie Creed-Miles, whom she met on the set of the film The Last Yellow, from 1999 to 2000. Their daughter, actress Esme, was born on 5 February 2000.

In 2004, Morton starred as a love interest in the dystopian film Code 46, directed by Michael Winterbottom and alongside Tim Robbins, and played the wife of a man who witnessed a deadly accident in the drama Enduring Love, opposite Rhys Ifans and Daniel Craig. Critics were polarized for the latter film and suggested that Morton did not have enough time on screen. Nevertheless, she earned a nomination for the Best Supporting Award at the 2004 British Independent Film Awards. In River Queen (2005), she took on the role of a young Irish woman finding herself on both sides of the wars between British and Maori during the British colonisation of New Zealand. The film was a box office success at the New Zealand box office, grossing around NZ$1 million in the country. For her role, she received a nomination for the New Zealand Screen Award for Best Leading Actress. She starred alongside Johnny Depp in the little-seen period drama The Libertine, and appeared in the drama Lassie, both of which were also released in 2005.

In 2006, she played the Moors murderess Myra Hindley in the television film Longford. Set between 1967 and 1997, the film depicts the relationship between the child murderer and Lord Longford, the politician who spent years campaigning (ultimately unsuccessfully) for her release. Longford was a critical success and premiered with 1.7 million viewers. Morton, however, was severely criticised by the relatives of the children who were killed by Hindley and Ian Brady, but she insisted, “It is my duty as a performer to raise issues […] we’re afraid to look at”. She received a Best Supporting Actress nomination at the 59th Primetime Emmy Awards, and won at the 65th Golden Globe Awards.

Morton took on roles in four feature films in 2007. She starred as a struggling police officer in the romantic drama Expired, and portrayed a Marilyn Monroe impersonator in the dramedy Mister Lonely. Morton worked again with director Anton Corbijn in the biographical film Control, where she appeared as Deborah Curtis, wife of musician Ian Curtis from the band Joy Division, whose biography Touching from a Distance formed the basis of the film. The film was acclaimed by critics. Roger Ebert remarked that Morton was “absolutely convincing as a plucky teenage bride”, and Variety magazine found her performance to be “astonishing” and “sympathetic”. For Control, she was nominated for the BAFTA Award for Best Actress in a Supporting Role. Her last film of 2007 was another biopic, Elizabeth: The Golden Age, in which she played Mary, Queen of Scots.

As of 2007, Morton was in a relationship with filmmaker Harry Holm (son of actor Ian Holm), whom she met while filming a music video for the band the Vitamins. Their daughter, Edie, was born on 4 January 2008, and their son, Theodore, was born in 2012. They live in Monyash, Derbyshire.

She made part of an ensemble cast in Charlie Kaufman’s postmodern drama Synecdoche, New York (2008), alongside Philip Seymour Hoffman, Michelle Williams and Emily Watson. In the film, she portrayed Hazel, one of the women in the life of a theatre director (Hoffman) whose extreme commitment to a realistic stage production begins to blur the boundaries between fiction and reality. As her character ages from 30 to 64 over the course of the story, Morton used full-face prosthetic makeup. She discovered that she was pregnant during the filming, which had a schedule that took up to 20 hours a day. The film was a box office bomb, but garnered praise from critics, appearing on many top ten lists of the year. Morton and her co-stars were eventually nominated for the Best Ensemble Performance award at the 18th Gotham Independent Film Awards. Also in 2008, she starred in The Daisy Chain, an Irish horror film about a couple who after the death of their daughter, take in an orphaned girl, only to become involved in a series of strange occurrences. It premiered at the 16th Raindance Film Festival (London; October 2008), and received a DVD release in 2010.

In early 2008, Morton revealed that she had been “close to death” after suffering a debilitating stroke due to being hit by a piece of 17th-century plaster that fell on her head (damaging her vertebral artery) in 2006. She was in hospital for three weeks after the incident. She withdrew from the public spotlight and took an 18-month break from film acting in order to learn to walk again.

In 2008, she was part of the Vodafone Foundation’s World of Difference campaign, which gives people the opportunity to work for a charity of their choice. Whilst attending a fundraiser for the charity Medical Aid for Palestinians (MAP) in January 2009, she vowed never to work for the BBC again after their refusal to broadcast an emergency charity appeal for the victims of Israel’s attack on Gaza on 27 December 2008. She was later joined by Tam Dean Burn, Pauline Goldsmith, Peter Mullan, and Alison Peebles, who also threatened to boycott the Corporation. In 2009, she also fronted a television advertising recruitment campaign for social workers in the UK.

Morton’s other project of 2009 was her directorial debut, the semi-autobiographical Channel 4 drama The Unloved, which follows an eleven-year-old girl (played by Molly Windsor) growing up in a children’s home in the UK’s care system, and shown through her perspective. Morton wrote the story in collaboration with Tony Grisoni, and The Unloved was first broadcast on 17 May 2009, drawing nearly 2 million viewers. It premiered at the Toronto International Film Festival in September 2009. Michael Deacon, for the Daily Telegraph, praised Morton on creating an “intense” and “vivid” dramatic film. Morton won a BAFTA for her direction in 2010.

Having been raised in the foster care system, Morton has often been active in causes involving the matter. In March 2009, Morton returned to her hometown to show her support for its children’s homes and protest against the threatened closure, by Nottingham City Council, of one of the four establishments with 24 social-care staff facing redundancy. In 2012, Morton showed her support for the Fostering Network’s annual campaign Foster Care Fortnight, and in September 2014, triggered by the Rotherham child sexual exploitation scandal, she discussed in a video interview the sexual abuse she experienced while in the foster care system as a child in Nottingham and that the police took no action when she reported the abuse. Morton had discussed the abuse previously while promoting the semi-autobiographical drama The Unloved, in an article for The Guardian.

In 2011, Morton wrote an open letter hoping her stepfather would get back in touch with her after being estranged for several years. However, it was revealed shortly afterward that her stepfather had died of prostate cancer four years prior.

On 20 July 2011, Morton received an honorary Doctor of Letters (DLitt) from Nottingham Trent University, “in recognition of her internationally successful acting career”.

Following a three-year hiatus from the screen to focus on her personal life and family, Morton returned in 2012. She provided the voice of Sola in the science fiction film John Carter, based on A Princess of Mars, which received mixed reviews and flopped at the box office. She next played a chief of theory in the thriller Cosmopolis, directed by David Cronenberg. Her role, described as “misjudged” by The Guardian, earned her the Best Actress in a Canadian Film Award at the Vancouver Film Critics Circle. She also served as a jury member at the 69th Venice International Film Festival in 2012.

Morton was the original voice of the artificially intelligent operating system in the 2013 romantic science fiction drama Her directed by Spike Jonze, but in post-production, she was replaced by Scarlett Johansson. She is, however, credited as an associate producer. Morton starred in the independent drama Decoding Annie Parker (2013) opposite Helen Hunt, playing a woman with breast cancer. The film was released in limited theaters, to mixed reviews from critics. Nevertheless, Betsey Sharkey of Los Angeles Times observed that the actress “gives Parker such a humility within a warm humanity that you feel an obligation to stick with her through the mounting horrors”. She was awarded the Best Actress Golden Space Needle Award at the 2013 Seattle International Film Festival.

In 2015, Morton starred as a mother in the First World War context in Cider with Rosie, a made-for-television adaptation of the book of the same name by Laurie Lee, and took on the role of an insurance investigator charged with recovering stolen diamonds in the European limited television series The Last Panthers, inspired by the notorious Balkan jewel thieves the Pink Panthers. Morton found her character to be a “very truthful, […] strong woman” and described her as a “female Bond”. Genevieve Valentine, for The AV Club, wrote: “Morton might at first seem a tough sell as someone so hard-boiled, but the taciturn, untouchable edifice she presents is leaking just enough poison at the edges that we look forward to watching her strike—the sort of character a six-hour miniseries was made for”.

Beginning in 2017, Morton has starred in the Hulu period drama series Harlots. She portrays Margaret Wells, the madam of a low-class brothel who seeks to improve her fortunes. The response from critics and audiences has been highly positive. The Telegraph found her to be the “standout performer”, and The Atlantic noted: “While the role doesn’t give Morton the same room to flex her acting muscles as, say, Woody Allen’s Sweet and Lowdown, she gives depth and moral conflict to a character who could easily be a pantomime dame in the wrong hands”.

As of 2019, Morton appears in the role of Alpha in The Walking Dead. Alpha is the villainous leader of the Whisperers, a mysterious group of survivors of a zombie apocalypse who–as a method of self-concealment–wear skins taken from the undead.