Sia Kate Isobelle Furler was born on 18 December 1975 in Adelaide, South Australia. Her father, Phil Colson, is a musician, and her mother, Loene Furler, is an art lecturer. Sia is the niece of actor-singer Kevin Colson. Sia said that as a child she imitated the performing style of Aretha Franklin, Stevie Wonder and Sting, whom she cites as early influences. She attended Adelaide High School. In the mid-1990s, Sia started a career as a singer in the local acid jazz band Crisp. Sia collaborated with the band and contributed vocals to their album Word and the Deal (1995) and EP Delirium (1997). In 1997 Crisp disbanded, and Sia released her debut studio album, OnlySee, on Flavoured Records, in Australia, on 23 December. The album sold about 1,200 copies. Unlike her later albums, OnlySee was marketed under her full name, "Sia Furler". It was produced by Jesse Flavell.
After Crisp disbanded in 1997, Sia moved to London, where she performed as a background vocalist for British band Jamiroquai. She also provided lead vocals for English downtempo group Zero 7 on their first three studio albums and toured with the group. On Zero 7's 2001 album Simple Things, Sia contributed vocals to two tracks including the single "Destiny", which peaked at No. 30 on the UK Singles Chart. In 2004, she provided vocals for Zero 7 on "Somersault" and "Speed Dial No. 2" (from the album When It Falls). In 2006, Sia again collaborated with Zero 7 for the group's third album, The Garden and hence she is regarded as the "unofficial" lead singer of Zero 7.
In 2007, Sia released a live album titled Lady Croissant, which included eight live songs from her April 2006 performance at the Bowery Ballroom in New York and one new studio recording—"Pictures". A year later, she left Zero 7 on good terms to focus on her solo career and was replaced by Eska Mtungwazi as the band's frontwoman. Sia released her fourth studio album, Some People Have Real Problems on 8 January 2008. The album peaked at No. 41 in Australia and was certified gold by the Australian Recording Industry Association. It charted at No. 26 on the US Billboard 200, becoming Sia's first to chart in the United States. Some People Have Real Problems yielded four singles, including "The Girl You Lost to Cocaine". It peaked at No. 11 in the Netherlands and No. 12 in Spain; it additionally reached No. 8 on the US Hot Dance Club Songs. Another single from the album was "Soon We'll Be Found".
Following the success of We Are Born, Sia became uncomfortable with her growing fame. She later told The New York Times: "I just wanted to have a private life. Once, as my friend was telling me they had cancer, someone came up and asked, in the middle of the conversation, if they could take a photograph with me. You get me? That's enough, right?" She refused to do promos for her tours, began to wear a mask on stage and became increasingly dependent on drugs and alcohol on the road; she considered suicide. Sia fired Enthoven and hired Jonathan Daniel, who suggested that she write songs for other artists.
In an interview with NME in February 2015, Sia revealed that she had completed the follow-up to 1000 Forms of Fear, entitled This Is Acting. The album was another collaboration with producer and co-writer Greg Kurstin. Furler said that she released 1000 Forms of Fear to free herself from her record deal and had planned simply to write for other artists, but the album's success spurred her to continue writing her own music. The same month, alongside the digital deluxe release of 1000 Forms of Fear, she released a mobile game, Bob Job. "Alive" from This Is Acting was co-written by Adele and had originally been intended for Adele's third album.