Larsson won the 2008 season of Talang, the Swedish adaptation of Got Talent, at the age of 10, winning 500,000 kronor. "My Heart Will Go On", the song she sang in the final, originally sung by Celine Dion, was later released that year as Larsson's debut single, charting at the official Swedish Singles Chart, Sverigetopplistan, for six consecutive weeks and peaking there at number seven for one week. She started singing on Sommarkrysset ("The Summer Cross"), another Swedish TV program.

Between December 2009 and January 2010, Larsson participated in a reality TV series called Jag ska bli stjärna (English: "I shall become a star") where she and other young Swedish talents got help on the difficult road to international fame and success. She was managed by Laila Bagge, and they flew to Los Angeles in the United States where they visited and talked with Disney and the three big record label companies - Universal Music Group, Sony Music, and Warner Music Group - but she did not get a contract offer anywhere, which Larsson later attributed to her age at that time.
Larsson signed with TEN Music Group in 2012 to record her debut compilation recording. The recording, the extended play (EP) Introducing, was leaked on 9 December 2012 through an unofficial music video of "Uncover" on YouTube, a static-view video featuring her singing the whole song in the recording studio in one whole continuous take. The five-song EP was released in Scandinavia on 21 January 2013, consisting exclusively of original songs. "Uncover" was released as the EP's lead single. It peaked at number one on both the Sverigetopplistan and DigiListan charts, as well as reaching number one in Norway and peaking at number three in Denmark, and by 25 February 2013, the song was certified platinum in Sweden by Universal Music Sweden as a result of the song having received over five million streams. The song entered the Svensktoppen track lists. In July 2013, at Sommarkrysset in Gröna Lund, she received a 3× platinum award for Introducing for selling over 120,000 copies in Sweden.

On 27 March 2013, Larsson's next EP was revealed through a music video of "She's Not Me (Pt. 1)" on YouTube. The five-song EP, Allow Me to Reintroduce Myself, was released in Scandinavia on 5 July 2013. "She's Not Me" (consisting of "She's Not Me (Pt. 1)" and "She's Not Me (Pt. 2)") was released as a double-single on 25 June 2013. On 3 April 2013, Larsson revealed on her blog that she had signed a three-year contract with Epic Records in the United States. On 11 December 2013, Larsson performed at the Nobel Peace Prize Concert in Oslo. On 1 October 2014, Larsson released her Scandinavian debut studio album 1, including the songs "Uncover", "Bad Boys" an…

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In 2015, Larsson planned and hosted a summer speech broadcast on Sveriges Radio, one of 58 celebrities that year. The 48-minute speech was broadcast live on the P1 channel on 25 July 2015, at 13:00 CET. Larsson was 17 at the time, which made her the youngest such speaker, surpassing Robyn and Gina Dirawi at age 20. In the speech, she talked about her life, her music career, her feminist views, others' reactions to her, and her feelings about all of it.

Between 2017 and 2019, she dated British model Brian H. Whittaker, whom she tweeted in 2015, but did not meet until two years later. Since 2020, Larsson has been in a relationship with Swedish-American dancer Lamin Holmén.

On 18 May 2017, Larsson released an H&M collection containing various garments and accessories. She was involved in the creation process by making decisions about press, colors and fitting. Pink is the common color throughout the entire collection.
Larsson has grown increasingly vocal with her views on other artists and industry workers with whom she works and admires. While she has high praise for performers such as Beyoncé, she is equal in her opposing views of such artists as Dr. Luke and Chris Brown. Larsson, a fan of Beyoncé, identifies as a feminist and models herself an "activist" after the singer. She attributes her openness of opinion on social media and in interviews to her parents, claiming: "Both my parents are very educated when it comes to social issues and being woke about what's going on in the world, and they've been very supportive of me having a voice".

In January 2015, Larsson gained a lot of positive attention in Sweden and the United States after posting a picture on her Instagram showing a condom wrapped around her leg and foot to refute the idea that penises can be too big for condoms to fit around. She has since 2019 been fronting a new campaign from Durex and AIDS organization (RED) promoting sexual health awareness and raising money for AIDS treatment in South Africa.

In order to increase public understanding of incontinence, she has openly stated that she used diapers until she was seven years old.

In June 2015, she came into the spotlight in her home country for openly questioning whether the Bråvalla Festival had any gender perspective whatsoever, as its promotion and performance line-up were highly dominated by male artists. She also wondered why she wasn't presented among the main acts despite being the most popular artist on Spotify of the festival's acts. That same day, Swedish singer Günther wrote on his Facebook profile criticizing Larsson: "You are one of many teenybopper chicks who are world-famous in Sweden and maximally hyped but don't come with any hits, only a lot of fuss." During her performance at the festival she countered back saying: "Fuck Günther, fuck all woman haters". This led to the hashtag #backazara being created and popularised on social media platforms, where thousands of people, including famous Swedish people, showed their support for Larsson.

On 11 May 2021, Larsson posted an image of text on her Instagram where she criticised Israel for killing civilians and "upholding apartheid", and expressed th…

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Larsson is mainly a pop singer. She has experimented with electropop, house, and dance music. Additionally, she is influenced by R&B.

She has cited Beyoncé as her biggest musical influence. Larsson's Swedish influences include Robyn, Seinabo Sey, Sabina Ddumba and her sister Hanna Larsson, with her neo soul group Lennixx. Additionally, her international influences include Christina Aguilera, Rihanna, The Weeknd, Jay-Z, Nicki Minaj, Ariana Grande, Jhené Aiko, and Lady Gaga. During her childhood, Larsson's mother listened to Whitney Houston, Etta James, Celine Dion and Aretha Franklin.