Looking for more mature roles, Roberts went on to obtain both supporting and lead roles in Lymelife (2009), 220.127.116.11. (2010), Scream 4 (2011), Adult World (2013), We're the Millers (2013), Palo Alto (2013) and The Blackcoat's Daughter (2015). She starred in the lead role of Chanel Oberlin on the Fox television series Scream Queens, as well as playing main roles in two seasons of American Horror Story.
Roberts was born in Rhinebeck, New York, to Kelly Cunningham and actor Eric Roberts. Her parents separated when she was a baby. Through her father's marriage, she is the stepdaughter of Eliza Roberts. Through her mother's marriage, she is the stepdaughter of musician Kelly Nickels. She has a maternal half-sister, Grace. Her paternal grandmother was acting coach Betty Lou Bredemus (1934–2015), and her aunts are actresses Julia Roberts and Lisa Roberts Gillan. During her childhood, Roberts spent time on the sets of her aunt Julia's films. These experiences sparked a desire to follow her father and aunts into the film industry. Her mother initially wanted her to have a normal childhood.
Roberts made her acting debut at age nine in Ted Demme's 2001 drama film Blow. It was the first film for which she ever auditioned. In the film, she portrayed Kristina Jung, the daughter of Johnny Depp's character (cocaine smuggler George Jung). That year, she also had a role in Leif Tilden's 10-minute short bigLove, and was an uncredited extra in some scenes featuring her aunt Julia Roberts in America's Sweethearts. Roberts went on to appear in smaller roles in two family films: in 2002's Grand Champion, as the sister of the main character Buddy (Jacob Fisher); and in 2003's Spymate, as the kidnapped daughter of former secret agent Mike Muggins (Chris Potter), who tries to rescue her with the help of a spy monkey. Grand Champion had a brief theatrical release in August 2004, while Spymate was not released until February 2006, when it was given a theatrical run in Canada, followed by its DVD release in April 2006.
In 2004, she began starring as the lead character Addie Singer in the Nickelodeon series Unfabulous, which debuted in September of that year. The sitcom earned Roberts a Teen Choice Award nomination and several Young Artist Award nominations. The series focused on a seventh grader, Addie, and her two best friends. It aired for three seasons (2004–07). The show also spawned TV movies, including The Perfect Moment. Also in 2004, Roberts guest-starred in an episode of the Nickelodeon series Drake & Josh titled "Honor Council". After her run on Unfabulous, Nickelodeon had considered giving Roberts a kick start into a music career. In 2006, Roberts returned to the big screen, starring alongside Sara Paxton and singer JoJo in Aquamarine. She won a 2007 Young Artist Award for Best Supporting Young Actress in a Feature Film for her role in the film. The film Aquamarine took fifth place at the box office in its opening weekend making $8 million. In early 2006, Roberts finished shooting her title role in Nancy Drew. The film was released to theaters on June 15, 2007, and grossed over $7 million in its opening weekend, though the film was not well received by critics. Roberts was set to reunite with Nancy Drew director Andrew Fleming on both Rodeo Gal and a Nancy Drew sequel in 2007, but these films were never made.
In 2008, she had her voiceover debut when she voiced the English version of the character Wilma in the CGI-animated family film The Flight Before Christmas. In 2009, Roberts starred alongside Jake T. Austin in Hotel for Dogs, based on the novel by Lois Duncan. The film premiered in January 2009, and took fifth place in its opening weekend with over $17 million. The film has to-date grossed over $114 million, and received generally mixed reviews from critics. Roberts starred as the lead in the film Wild Child, about a rebellious teen from Malibu, California sent to a boarding school in England. Roberts described her character as "pretty much your typical spoiled-brat Malibu socialite who gets shipped off to a British boarding school." Roberts also appeared in the independent film Lymelife with Alec Baldwin, which was premiered at the 2008 Toronto International Film Festival.
In 2010, Roberts co-starred as Grace in the film Valentine's Day in which her aunt, Julia Roberts also appeared, although they were never together on-screen. She also appeared that year in Twelve and It's Kind of a Funny Story. The following year, she co-starred in the film adaptation of Memoirs of a Teenage Amnesiac. She also starred alongside Freddie Highmore in the romantic comedy The Art of Getting By. In 2011, she played the role of Jill Roberts in the Wes Craven film Scream 4.
In 2013, Roberts co-starred with John Cusack and Evan Peters in Adult World. Roberts played a recent college graduate who works at an adult bookstore to make ends meet. She has said that most of her lines were ad-libbed so her reactions in the film were completely genuine. Her performance was praised by both Andrew O'Hehir of Salon and Stephanie Zacharek of The Village Voice, who praised Roberts' performance as "both breezy and carefully tuned". Roberts appears in a supporting role in Dustin Lance Black's Virginia, which received a limited theatrical release in May 2012 after a two and a half year delay. She next appeared in the 2012 film Celeste and Jesse Forever, parodying pop stars such as Kesha with her performance as Riley Banks, an incurious blonde singer. Roberts said in an interview that her role as Banks tempted her to write an album of songs using her character as an alter ego.
On February 7, 2013, The Hollywood Reporter confirmed that Roberts had been cast to star in a pilot for Fox called Delirium, based on the Lauren Oliver novels. She portrayed Lena Haloway, the protagonist, but Fox decided not to pick up the show. Roberts then starred in the comedy film We're the Millers, alongside Jennifer Aniston and Jason Sudeikis. It was released on August 7, 2013. The film received mixed reviews from critics and was a financial success, grossing over $269 million against a budget of $37 million. She next appeared in season three of the FX horror anthology series American Horror Story, called American Horror Story: Coven, from late 2013 through January 2014. Roberts portrayed a self-involved party girl named Madison Montgomery, who also happens to be a telekinetic witch. She then portrayed Maggie Esmerelda, a con artist posing as a fortune teller, in the season four, called American Horror Story: Freak Show.
Roberts played the lead role in Gia Coppola's directorial debut, Palo Alto, based on James Franco's short story collection of the same name. The film was released in May 2014 to generally positive reviews, with particular praise for Roberts' performance. Tom Shone of The Guardian and Ian Freer of Empire both called her the "standout" of the film, with Freer praising her performance for being "heartbreaking as she suggests longings and anxieties without over-hyping it. Much like the film itself." Roberts then starred alongside Palo Alto co-star Nat Wolff in Ashby, portraying the supporting role of Eloise. The film had its world premiere at the Tribeca Film Festival on April 19, 2015, and was released on September 25, in a limited release and through video on demand.
Roberts next appeared in the horror film The Blackcoat's Daughter (also known by its original title February) alongside Kiernan Shipka. Directed by Osgood Perkins, the film premiered at the 2015 Toronto International Film Festival. Roberts plays the lead character Chanel Oberlin on the first season of Fox's horror comedy series Scream Queens, alongside Jamie Lee Curtis and Lea Michele. The series was created by American Horror Story producers Ryan Murphy and Brad Falchuk, with Glee producer Ian Brennan. She reprised this role in the second season of Scream Queens the following year. It was later cancelled after two seasons. In 2016, Roberts starred alongside Dave Franco in Lionsgate's adaptation of the young-adult novel Nerve.
In June 2016, the Human Rights Campaign released a video in tribute to the victims of the 2016 Orlando gay nightclub shooting; in the video, Roberts and others told the stories of the people killed there.
On August 1, 2017, Ryan Murphy announced Roberts' return to American Horror Story, in its seventh season, Cult, via his personal Instagram account.
In 2005, Roberts released a debut album titled Unfabulous and More. The album was released on September 27, 2005, through Columbia Records and Nick Records. It also served as the soundtrack to the television series Unfabulous, in which Roberts starred. The album peaked at number 46 on Billboard's Top Heatseekers chart. In September 2005, two promotional singles were released from the album: "I Wanna Be" and "Dummy". The album includes several original songs (among them "Dummy" and "I Wanna Be", both of which were also released as music videos, "I Have Arrived" and "This Is Me", which was co-written by Roberts), as well as some of Addie's songs from the first season, including "Punch Rocker" and "New Shoes" (both from the episode "The Party"), "94 Weeks (Metal Mouth Freak)" (from "The Bar Mitzvah") and "Mexican Wrestler" (which had previously appeared on Jill Sobule's 2000 album Pink Pearl and in the episode "The 66th Day" from Unfabulous). During the same year, Roberts recorded "If I Had It My Way" for the soundtrack of the 2005 Disney film Ice Princess. In 2006, Roberts covered the song "Island in the Sun", which was originally recorded by Weezer in 2001; she recorded the song for the Aquamarine soundtrack, a film in which she starred as one of the leads.
Roberts said in a 2007 interview: "Right now I am focusing on movies. I am getting ready to start a new movie this summer so that is taking a lot of my time. I think when I am a little bit older it is definitely something I'd like to pursue." In another interview, she said: "My musical career is indefinitely on hold. I don't like people who become like 'actor slash singer.' I think people should be one or the other because usually you're not going to be great at both. You're going to be better at one, so you might as well stick to the one you're good at. I'm going for acting."
In September 2011, Roberts began attending Sarah Lawrence College but by January 2012, she had put her studies on hold to concentrate on work commitments.
Roberts began dating actor Evan Peters in 2012 after they worked together on the film Adult World. In July 2013, while they were staying at a hotel in Montreal, Quebec, someone overheard a dispute coming from their room and called the police. After a "heated argument", they had begun hitting each other. When the police arrived, they arrested Roberts. Peters was not arrested because Roberts did not have any immediately visible injuries. Peters declined to press charges and Roberts was released several hours later. In a joint statement, the couple called it "an unfortunate incident and misunderstanding," and stated that they "are working together to move past it." Peters confirmed in March 2014 that he and Roberts were engaged. From March 2014, Peters and Roberts have been in an off/on again relationship, eventually leading to their breakup in late May 2016. In January 2017, Roberts confirmed she was engaged to Peters once again.
In February 2009, Roberts was named the brand ambassador for Neutrogena, appearing in print and television ads for the company. Roberts has also appeared multiple times as part of Teen Vogue's Best Dressed list, including June 2007, September 2008, December 2008 and February 2009.