Isabella May Ramsey was born in Nottingham on 25 September 2003.^[2][3][4] They began their education in Leicestershire before transitioning to the online school King's InterHigh at age 12,^[5] as they "really didn't enjoy mainstream secondary school and wasn't happy". The shift to a flexible learning environment allowed Ramsey to balance education with their acting career.^[6][5]

Growing up, Ramsey enjoyed art, music, writing and football, while performing with local amateur theatre groups, including Stagecoach Theatre Arts, from a young age.^{[7][8][9][10][11]} At age 10, Ramsey joined the Television Workshop in Nottingham,^[12][13] which provided training and support for early auditions, including for Game of Thrones.^[14] Ramsey credits the Workshop for shaping their approach to acting: "[it] teaches you to be and become. No pretending."^[15]

From 2016 to 2019, Ramsey portrayed Lyanna Mormont in the HBO fantasy drama television series Game of Thrones. The part is Ramsey's first credited role. After their debut appearance in the sixth season episode "The Broken Man", fans and critics noted Ramsey was a standout actor for portraying their character's no-nonsense leadership style.^[16][17] Co-showrunner D.B. Weiss said Lyanna was "only ever meant to be in one scene, not a prominent supporting character for multiple seasons," but after they realized Ramsey's performance, "that we would not be doing our jobs if we kept her as a one-scene character."^[18] This reaction was repeated after their appearance in the season finale,^[19] with The Hollywood Reporter calling them "season 6's breakout star".^[20] Ramsey continued in the role for the series's seventh and eighth seasons.

Ramsey starred as Mildred Hubble in the CBBC fantasy drama series The Worst Witch (2017–2019),^[16] for which they won the Young Performer award at the 2019 British Academy Children's Awards.^[21] Their role was recast with Lydia Page for the fourth and final season.^[22] Ramsey portrayed Miranda, a rebellious teenager, in the psychological drama film Two for Joy (2018),^[23] and voiced the title character in the Netflix original series Hilda. The series marked the debut of Ramsey's singing talent, with their debut song "The Life of Hilda" released on 25 November 2020.^[24] They reprised the role of Hilda in the 80-minute movie special, Hilda and the Mountain King, which premiered on 30 December 2021.^[25] For their role in Hilda, Ramsey was nominated for Best Voice Performance at the British Animation Awards in 2020 and 2022.^[26][27]

In 2020, Ramsey was cast in the second season of His Dark Materials as Angelica, a young girl from the world of Cittàgazze.^[28] Ramsey portrayed Elsbeth in the biographical drama Resistance (2020), which explores how Marcel Marceau helped Jewish children escape Nazi persecution during World War II. Ramsey was drawn to the film because "the script didn't shy away from the reality of war [in] telling such an important story".^[29] TheWrap's Michael Nordine praised Ramsey's performance as "affecting", noting "great things can be expected of the teenage thespian in the future".^[30] In 2021, they appeared in the lesbian horror short film Requiem alongside Safia Oakley-Green.^[31] Ramsey starred in their first leading film role as Lady Catherine in Catherine Called Birdy (2022), a medieval coming-of-age comedy written and directed by Lena Dunham and adapted from Karen Cushman's novel. Rolling Stone's David Fear hailed Ramsey as "a gift from the casting gods".^[32] Ramsey wrote and performed "Birdy Song" for the film's soundtrack.^[33]

In February 2021, Ramsey was cast in the lead role of Ellie for the HBO adaptation of the 2013 video game The Last of Us alongside fellow Game of Thrones alumnus Pedro Pascal.^[34] They received the news during production on a different project.^[35] Ramsey's performance and chemistry with Pedro Pascal's Joel received praise.^[36][37][38] For the first season in 2023, they received several awards nominations, including at the 81st Golden Globe Awards,^[39] 75th Primetime Emmy Awards,^[40] and 39th TCA Awards.^[41] Ramsey's second-season performance in 2025 was praised;^[42][43][44] they were nominated at the 77th Primetime Emmy Awards in 2025, making them the youngest two-time lead drama actress nominee.^[45]

In 2023, Ramsey portrayed Kelsey Morgan, a pregnant heroin addict, in the second series of Time. Their performance was praised,^[46][47] and they won the Royal Television Society Award for Female Supporting Actor.^[48] They voiced Molly in Chicken Run: Dawn of the Nugget (2023), for which The Independent's Clarisse Loughrey praised their "joyous, buoyant performance".^[49] In April 2025, Madame Tussauds announced that Ramsey would receive a wax figure to be displayed at its museum in London,^[50] which was unveiled in September.^[51] Ramsey voiced the artificial intelligence system nTrac in the film The Correction Unit (2025).^[52] They are set to appear as the title character in Daisy Haggard's drama series Maya (2026),^[53] as lead character Ivy in George Jaques's comedy film Sunny Dancer,^[54] and as Ella in Guy Nattiv's psychological thriller Harmonia.^[55] In 2025, they worked on new music with singer-songwriter Matt Maltese.^[56]

Ramsey identifies as non-binary.^[57][58] While they stated that they/them pronouns are "the most truthful thing for me",^[59] they are indifferent to which pronouns are used for them,^[60][61] telling others to "call me how you see me".^[1] Ramsey considered withdrawing from Emmy consideration due to the lack of non-gendered categories but decided to contend for Lead Actress after discussions with Craig Mazin, not wanting limited language to prevent celebrating non-binary performers;^[62] Ramsey's was the second non-binary acting nomination^[63] and the first for a leading role^[64] at time of nomination,^[b] and their second-season nomination made them the first non-binary performer to be nominated more than once.^[67] In 2025, Ramsey became the first non-binary person to receive a wax figure at Madame Tussauds.^[50]

In September 2023, Ramsey was included on Time's 100 Next list; fellow non-binary actor Emma D'Arcy praised their acting skills and called them "an inspiring figure in the LGBTQIA+ community".^[68] Regarding their sexuality, Ramsey said they are "not 100 per cent straight. I'm a little bit wavy".^[59] Ramsey plays the guitar and sings.^[69] They wore a breast binder 90% of the time they filmed The Last of Us, saying it helped them "concentrate" although it "probably isn't healthy".^[70] While filming The Last of Us, they developed a close friendship with actor Pedro Pascal;^[71][72] Ramsey found the second season "a lonelier experience" due to their separation.^[73]

Ramsey is Christian and says that their faith helped in their struggle with anorexia nervosa. They took part in a "full-immersion" baptism.^[74] In 2020, they ran a YouTube channel and related Instagram account called United Hope where they shared their faith.^[74][75][76] Ramsey's faith became "a lot quieter" by 2023.^[77]

Ramsey is a vegetarian, self-described as "vegan-ish";^[78] they were vegan for a number of years, having been raised as pescatarian,^[79] though they occasionally eat free-range eggs due to allergies.^[80] They are an outspoken advocate for veganism.^[81]

Ramsey was diagnosed as autistic when they were 18, while filming the first season of The Last of Us. They called the diagnosis "freeing", explaining "It enables me to walk through the world with more grace towards myself about not being able to do the easy everyday tasks that everyone else seems to be able to do".^[82] They said being neurodivergent has "massively" influenced their career and performances^[83][84] and that they "wouldn't be an actor if it wasn't for [their autism]", citing their "insane levels of visual perception".^[85]

Ramsey has used their platform to support the Palestinian cause.^[86] They signed a Queer Artists for Palestine letter calling for a ceasefire in Gaza, condemning "pinkwashing", and pledging to "stand firmly with [Palestinians] in their call for dignity and self-determination" and boycott Israel.^[87]

In response to the April 2025 UK Supreme Court ruling in For Women Scotland Ltd v The Scottish Ministers on the definition of woman in the Equality Act 2010 and subsequent EHRC guidance, Ramsey was one of over 400 film and television professionals to sign an open letter pledging "solidarity with the trans, non-binary and intersex communities" and condemning both actions.^[88]