Thorne was born in Pembroke Pines, Florida, to Tamara Thorne (née Beckett) and Delancey Reinaldo "Rey" Thorne. She has three elder siblings, half-sister Kaili, Danielle, and Remy, who are also actors. Her father, who died in 2007 in a traffic accident, was Cuban. On her maternal side, Thorne said she is of Italian ancestry, with some Irish, English, Welsh, and German influences. Thorne has said that she was raised by a single mother who was supporting four children, and that they were very poor, which is why she worked as a child actor, to help to support the family.
In 2010, Thorne replaced Jolean Wejbe as Tancy "Teenie" Henrickson, Bill and Barb's younger daughter in Season 4 of HBO's Big Love. Thorne starred as co-star on the Disney Channel sitcom Shake It Up, originally titled Dance, Dance Chicago. Thorne played CeCe Jones, a dancer with heavy ambitions for a career in the spotlight despite having dyslexia. The show is a buddy comedy centered on a teen dance show (in a show-within-a-show format) co-starring Thorne and Zendaya. The multi-camera series began production in Hollywood, California, in July 2010 and premiered on November 7, 2010, on Disney Channel. While she had a substantial portfolio of work in television and film, Thorne had no experience in professional dancing before being cast. After signing onto the show in October 2009, she began taking three dance classes every night. Thorne's first single, "Watch Me" was released on June 21, reaching 86 on the US Billboard Hot 100 charts, 9 on the US Top Heatseekers charts and earning RIAA: Gold. On September 29, 2011, Disney Channel announced it had increased Shake It Up's second season order to 26 episodes. A 90-minute special episode "Made In Japan" aired August 17, 2012, as the season two finale.
On June 4, 2012, Disney Channel announced that Shake It Up had been renewed for a third season. In 2012, Thorne was cast as Avalon Greene in the Disney Channel Original Movie Frenemies. "TTYLXOX" was released on March 6, reaching 97 on the US Billboard Hot 100 charts. On March 30, 2013, it was confirmed by Hollywood Records via Twitter that Thorne had officially signed to the record label. On July 25, 2013, the Disney Channel confirmed that Shake It Up would be canceled after the end of the third season. On April 23, 2013, Thorne announced her debut album with eleven songs. Thorne spoke about the album, saying "What fans can expect is [for it] just to be very different from anyone because I don't like to be one of those artists where you can be like: 'Oh yeah, I know them from that song.’ All my songs are very different from each other. So I don’t want to be known as only one genre.” Thorne cited Britney Spears, Kesha, and Destiny's Child as influences for the album.
In 2014, Thorne co-starred in the comedy Blended, with Adam Sandler and Drew Barrymore as Sandler’s character's daughter. She also co-starred in the films Alexander and the Terrible, Horrible, No Good, Very Bad Day (2014) and The DUFF (2015), playing high school antagonists. On July 30, Thorne was cast in an episode of the fifteenth season of the CSI. The episode, "The Book of Shadows", aired October 19, 2014. Thorne appeared in the sequel Mostly Ghostly 2: Have You Met My Ghoulfriend as Cammy Cahill, the love interest of Ryan Ochoa's character, Max Doyle. The film was broadcast as a Halloween special in October 2014. On October 15, Thorne revealed her debut album was canceled, saying she wasn't happy with the "auto-tuned bad music" she had in the works. She released an EP, Jersey, on November 17. The lead single from the EP, "Call It Whatever", debuted in the Billboard Hot Dance Club Songs chart at number forty-seven, eventually rising to number ten, spending a total of ten weeks on the chart.
It was reported that Thorne had signed a new deal to write a series of books, beginning with her first novel, Autumn Falls. Thorne has signed on, with Kyra Sedgwick, as the leads in Manis Film's thriller Big Sky; Thorne plays Hazel. On December 12, Thorne was cast in the MTV series Scream, which is a television adaptation based on the original slasher film series Scream. Thorne was offered the lead role of the series but felt that the role of the "mean, terrible Nina" would be more iconic. In 2015, Thorne was cast in the animated United States dub of the film The Frog Kingdom, portraying the role of Frog Princess opposite Drake Bell and Cameron Dallas. The film is scheduled to be released on video on demand and on DVD beginning on June 30, 2015, by Lionsgate Home Entertainment.
Thorne confirmed she signed on to star in the American adaptation of Midnight Sun, based on the original 2006 Japanese film Midnight Sun which is expected to premier on July 14, 2017. Also in 2015, she appeared as Ashley, a young and famous singer in Alvin and the Chipmunks: The Road Chip. In 2016, Thorne played Rain in Tyler Perry's Boo! A Madea Halloween.
In 2017, Thorne starred in the Netflix original film, You Get Me, opposite Halston Sage, Taylor John Smith, and Nash Grier. In October of that year, Thorne appeared in the slasher comedy The Babysitter, directed by McG and released directly to Netflix.
On August 23, 2016, Thorne came out as being bisexual on Twitter.