Stone began performing at the age of six, appearing in plays at elementary school. She developed an interest in professional acting three years later, a pursuit which her parents approved of, but briefly delayed. In an interview with the National Post, Stone’s mother stated, “It felt like it was important for Julia to spend another year becoming her before throwing herself into becoming other people.” Following a number of roles in student-produced films, Stone began booking independent features. Her first screen role was in the 2009 survival-horror short A Brush of Red, in which she played an unnamed character.

Stone’s breakthrough role came in 2011, when she was cast as an adoptee searching for her birth mother in The Year Dolly Parton Was My Mom. For her performance in the film, Stone won a Young Artist Award and critical acclaim. Liam Lacey of The Globe and Mail noted, “Young actress Julia Stone hits the right notes.” Nylon magazine declared that Stone was “about to break out in a big way.”

She appears in the opening scene of the 2012 series Emily Owens, M.D., playing a girl named Abbey who initially ridicules the main character, but later comes to admire her. Following other guest parts, and additional work in shorts, Stone booked her first role as a series regular in the TV show The Killing, which she appeared on in 2013. In an interview with The Huffington Post, she described winning the part as “one of the happiest moments of my life”. In the series, Stone plays a prostitute who becomes caught in a love triangle with her boyfriend and another girl. “It’s really raw, but it’s the kind of thing that’s happening and it’s important to put a light to it,” Stone said. “There wasn’t anything explicit or unnecessary and they shot it in a way that’s supportive to the story. My mom and I saw it similarly—this is an important story that needs to be told.” While discussing the character’s effect on her, Stone noted, “I really admire that no matter what, she’s believing and hoping and having faith in a better future. That’s something that I’ve taken away from this whole experience of playing her, is that no matter what, you can still always have hope. That’s something I’ve learned from her.”

In 2013, Stone described her interest in psychology as an asset in her work as an actress. To immerse herself in roles, she began listening to songs that she felt fit the tone of a scene after reading scripts, while also writing background stories about her characters.

Stone’s work in The Killing led to numerous opportunities in Canadian films. In 2014, she told the National Post, “I feel excited because I keep getting more opportunities to develop my craft and to do what I love. I just hope to be able to keep telling stories and playing characters that mean a lot to me.” Canadian director Lindsay MacKay cast Stone in the coming-of-age drama Wet Bum (also titled Surfacing). In the tale, she plays a social outcast who finds solace in swimming and develops unexpected bonds with numerous people. While discussing the film, Stone revealed that she identified with her character’s situation: “I think a lot of people have gone through something similar to what she’s gone through.”

Wet Bum premiered at the Toronto International Film Festival in 2014 and won critical acclaim. Courtney Small of Cinema Axis noted, “The confines of a swimming pool serve as the perfect metaphor for the awkwardness of adolescence,” and called Stone’s performance “outstanding.” Indie-Outlook.com proclaimed Stone “utterly mesmerizing.” Matt Fagerholm of RogerEbert.com declared that Stone had delivered “a stunningly raw and unmannered performance.” For her work in the role, Stone was chosen as a Toronto International Film Festival Rising Star, received recognition from E!, and won the Leo Award in the category of Best Lead Performance.

Stone had a minor role in the 2015 German film Every Thing Will Be Fine, with James Franco and Charlotte Gainsbourg. The picture generally received unfavorable reviews. She also guest-starred on the TNT series Falling Skies, playing a warrior.

In 2016, Stone starred with Dylan Authors in the film Weirdos, directed by Bruce McDonald. Like 2014’s Wet Bum, this film also premiered at the Toronto International Film Festival, and Stone was given top billing in promotional material. Set in 1976, the story follows Kit and his girlfriend Alice (Stone), who embark on a trip to find Kit’s mother. As the tale begins, Stone’s character is uninhibited and adventurous, but gradually matures as the film progresses. The Vancouver Sun noted, “It becomes clear watching Weirdos that the story is being told from Alice’s point of view, something Stone said she didn’t realize was happening during filming. The teen pair are on a trip into Kit’s past, but Stone’s Alice learns the most from the journey.” Variety labeled it a film of “self-discovery,” and also praised the performances. An article from RogerEbert.com declared, “What makes Weirdos worth a look, above all, is the performance by Stone, who has quickly emerged as one of the most promising actors of her generation.”

In November 2016, The Hollywood Reporter announced that Carlos and Jason Sanchez had cast Stone in Allure, opposite Evan Rachel Wood. The film follows an emotionally troubled 30-year-old woman named Laura who falls in love with Stone’s teenage character Eva, convincing Eva to live with her. Unlike Stone’s earlier work in The Killing, the narrative explores mental trauma, manipulation of a minor, and explicit sexual themes. An early review from the Toronto International Film Festival called the tale “a psychological thriller that focuses on a disturbing and obsessive relationship.”

In June 2018, Stone finished work on the dramatic film Honey Bee, in which she plays a sex-trafficking victim who enters foster care. Her performance earned her the 2019 Leo Award for Lead Female. Mark Hanson of In The Seats gave the film a mixed review, noting, “Stone commits to an all-consuming role that requires her to be in every scene but it’s too bad that most of her big moments end up feeling calculated like awards-show clips.” In a review for The Gate, Andrew Parker praised the film, declaring that it featured “Stone’s best performance to date.” Brad Wheeler, writing for The Globe and Mail, found the film average but noted that it was “worth seeing for Stone alone.” Norman Wilner of Now Toronto praised Stone’s performance, declaring that the film was “all the stronger for having her at the centre of it.”