Williams made her acting debut in 2011 as Arya Stark, a lead character in the HBO epic medieval fantasy television series Game of Thrones (2011–2019).

In 2019, Williams jointly developed and launched the social media platform Daisie, a multi-media networking app designed to be an alternative means to help artists and creators (especially those who are trying to get started) in their careers.

She later transferred to Bath Dance College to study performing arts, where she trained in musical theatre, ballet, pointe, tap, street, freestyle, gymnastics and trampolining, with the ambition of becoming a professional dancer.

[17][18][19][20] The character of Arya Stark is regarded as an anti heroine, a fan favourite that developed into one of the central protagonists in the Game of Thrones fantasy epic.

[42][43] In 2012, the second year of her professional acting career, she was submitted in the category of Outstanding Supporting Actress for the 64th Primetime Emmy Awards by HBO, but did not make the nomination shortlist.

[73][74][75] In 2017, Williams starred, alongside Bill Milner, as Lucy in the Netflix science fiction teen superhero thriller film iBoy.

"[77] Also in 2017, Williams appeared as Isabel Baxter in Mary Shelley a romantic period-drama film directed by Haifaa al-Mansour and written by Emma Jensen.

[84][85] The play did well at the box office and Williams' stage performance was regarded a critical success, with the production later being broadcast free on Instagram from 30 November to 3 December 2018 and again during the last week of March 2020.

[89][90] In 2019, Williams starred alongside Asa Butterfield and Nina Dobrev in the coming of age romantic comedy-drama film Then Came You, in which she played a teenager with a terminal illness.

[91][92][93] From 2019 to 2021 Williams has voiced the role Cammie MacCloud, a mischievous Scottish hacker, in the U.S. animated web series Gen:Lock that is set in a dystopian future, which is broadcast on the Rooster Teeth subscription service.

[96][97] The New York Times said Williams portrayed the Marvel superhero Rahne Sinclair / Wolfsbane—a Scottish mutant who can turn into a wolf, but struggles to reconcile this with her religious beliefs -- "with endearing sincerity".

[98] Though the film received mixed to negative reviews her performance was regarded as good by The Hollywood Reporter, including adding "layers of panache and emotion" to her character.

[96][100][101] Written and directed by Josh Boone, the film also stars Anya Taylor-Joy, Blu Hunt, Charlie Heaton, Alice Braga and Henry Zaga.

Action is set in motion following a seemingly harmless prank played on Kim of a fake video that makes her believe that everybody in the world has just two weeks to live.

[114] Dread Central felt that she gave better performance than she did in New Mutants and commented "it's undeniably cool to see the young, now forever iconic actress kick ass in a real world setting".

The film was directed by French director Julius Berg and adapted from the graphic novel Une Nuit De Pleine Lune by Belgian artist Hermann and writer Yves H.[116][117][118] Her veteran co-actor Sylvester McCoy predicted success for Williams beyond acting "she's full of energy – a little bubbly ball of fire and creativity... she's grown up in the business and she knows it inside out... She's a rising star as an actress, but I wouldn't be at all surprised if she became a director and a producer... She's got all those abilities and that intelligence and the knowledge of the business from years of doing it... from a young age.

The series is based on guitarist Steve Jones, 2018 memoir Lonely Boy: Tales from a Sex Pistol;[120] and was executively produced and directed by Danny Boyle.

[122][123][124] Williams' is underutilized but brings her "formidable screen presence" as the "untouchably cool" Jordan complete "with a vertical sheet of peroxide blonde hair.

"[128][129] Williams "sparkles" in the second episode's cold opening, when she recreates Jordan's cycling through her seaside home town and then commuting by train wearing a fully revealing transparent PVC top, to the consternation and heckling of the people around her, that straightforwardly presents punk movement's effect on society: a scene both The Guardian and Vogue judged to be one of the strongest in the series.

[130][131][132] Williams continued to embrace the punk-rock style for her Pistol press tour, thinking of her own public image the actress said that she was inspired by how Jordan used both her clothing and her physicality as a defiant presence, as a political statement that turned the male gaze in on itself and took control of the situation.

[142][143][144] In July 2020, she featured in the Apple MacBook's "Made in the UK" campaign ad celebrating UK-based creators alongside others including screenwriter and actor Michaela Coel, artist Grayson Perry, film maker Jenn Nkiru, animation studio Aardman, printmaker Gabriella Marcella, rapper Dave and singer Labrinth.

The aim was to promote the brands move to a circular fashion model where customers recycle unwanted garments, resulting in less waste and lower environmental impact H&M.

The fast-fashion brand recycling initiative was criticised for not going far enough, for not using sustainable materials from the outset, for perceived poor treatment of its workers and failure to meet the Living Wage targets they set themselves.

[148][149][150] Williams and Lowri Roberts, via their production company Rapt, teamed up with independent studio Delaval Film as executive producers on a 15-minute British/Czech co-produced stop motion animation short, Salvation Has No Name.

[151] Salvation Has No Name, to be screened at festivals in 2022, is a cinematic folktale that explores the issue of xenophobia and faith around the refugee crisis through a surreal performance of a troupe of circus clowns.

[155] Daisie is a multi-media social networking platform, designed to help artists and creators of all types and backgrounds from across the various creative industries to showcase their work, discover projects and collaborate and provide an alternative route to develop their careers.

[157][160] Users' profiles grow by connecting with other creative people (via "chains") and working collaboratively on projects (not by obtaining high follower popularity counts, friends, or likes typical of most other social media apps).

[157][162][163][159] Williams and Santry said that they designed Daisie as a tool for young people to bypass the obstacles, both internal and external, that prevent budding artists from gaining recognition and exposure.

[4][170][171][172] In 2019, Williams and her then-boyfriend Reuben Selby (ended in February 2023) started to appear on the fashion scene as a couple, regularly in co-ordinated ensembles.

[190][178] At the eve of COP26 November 2021, Williams (as the WWF Global Ambassador) delivered the opening address at the premiere of Sir David Attenborough's upcoming television series The Green Planet at Glasgow's Imax cinema.