In 2000, Sia signed to the Sony Music sub-label DancePool, whereupon she released her major-label debut, Healing is Difficult, an eclectic mix of R&B and jazz. The album included the underground club hits "Drink to Get Drunk" (remixed by Different Gear) and "Little Man". It also featured the single "Taken For Granted", a song containing a sample from Prokofiev's Dance of the Knights. The single reached #10 in the UK Singles Chart during June 2000.
Part of Sia's success can be attributed to the UK garage remix of "Little Man" by Wookie. It still remains a popular song in nightclubs throughout the UK. Healing is Difficult received wide critical acclaim and led to Furler being hailed as the next Lauryn Hill or Nelly Furtado by certain sections of the music press. However, following record label conflicts, Sia left Sony Music and signed with Go! Beat Records, a subsidiary of UMG.
2003 saw Sia release an EP entitled Don't Bring Me Down. This was used as the closing title track of the French film, 36 Quai des Orfèvres. Her second album, entitled Colour the Small One, was released in Australia and Europe the following year. This downtempo album saw Sia employ a mixture of acoustic instruments and electronic backing in her material, which led to comparisons to artists such as Dido and Sarah McLachlan. It featured "The Bully", which was a collaboration with American musician Beck Hansen. Two further songs were co-written and produced, but have yet to be released. Colour the Small One, though, spawned the singles "Breathe Me" and "Where I Belong". The latter track was earmarked to appear on the soundtrack of the film Spider-Man 2, but owing to a record label conflict, its inclusion was withdrawn. In anticipation of this notable inclusion, the single of "Where I Belong" was packaged with a cover featuring Sia dressed in a Spider-Man costume.
In early 2005, Sia parted company with Go! Beat Records, disappointed at the company's poor promotion of the album, and the failure of the label's U.S. counterpart to pick up the record. Meanwhile, "Breathe Me" was beginning to receive international notice with appearances on the series finale of the U.S. HBO television series Six Feet Under and the broadcast of the 2006 Victoria's Secret Fashion Show. The track had been licensed to Astralwerks (which also produces the Six Feet Under soundtracks), and based on positive feedback, the full license of Colour the Small One was picked up by Astralwerks and given an American release in early 2006.
Sia toured the U.S. throughout 2006, promoting the album and cross-promoting the Six Feet Under season five DVD release. The re-released 2006 U.S. album features four bonus tracks: "Broken Biscuit" (from the Don't Bring Me Down EP), "Sea Shells" (the B-side to "Breathe Me" in the UK) and two remixes of "Breathe Me" by Four Tet and Ulrich Schnauss.
In addition to her solo career, Furler provided vocals for Zero 7 on their hit singles "Destiny" and "Distractions" from their debut album, Simple Things. Zero 7's second album, When it Falls, featured Sia voicing "Somersault" and "Speed Dial No. 2". Their third album, The Garden (released May 2006), found six contributions from Furler, with two ("Throw it All Away" and "You're My Flame") released as singles in the UK and North America.
On November 25, 2005, Sia recorded a duet with singer Katie Noonan, a member of Brisbane-based band George. The song, entitled "Sweet One", was supposed to be included on the respective artists' solo albums in 2007 but has not appeared on the track listings of either Sia's Some People Have Real Problems or Noonan's Skin. Sia recorded a cover version of Radiohead's "Paranoid Android" in 2006, which appeared on the tribute album, Exit Music: Songs with Radio Heads. The song also appeared in an episode of teen drama The O.C..
In 2007, Sia had a prolific year in terms of releasing music, although she would not release her third full album until January 2008. On April 3, 2007, Sia's third LP (almost EP-ish) Lady Croissant was released in the U.S. It featured eight live songs and one new studio track ("Pictures"). In November 2007, Sia's four-song EP, Day Too Soon, was released on iTunes. It included the tracks "Day Too Soon", "Buttons", "The Girl You Lost to Cocaine", and a remix of "Day Too Soon" by Mock & Toof.
Sia's fourth LP (third proper), Some People Have Real Problems, was released in January 2008. The first single was "Day Too Soon". A video for the song "Buttons" can be found on YouTube, as well as many other live and studio videos. The song "Little Black Sandals" from the the album was featured on the television show Private Practice in the season one episode, "In Which Addison Finds a Showerhead".
On 8 January 2008, Sia performed "The Girl You Lost to Cocaine" on Late Night with Conan O'Brien. The song has also been remixed by the likes of Sander van Doorn, Stonebridge and Jens O. The Sander van Doorn remix was a hit in the Netherlands, reaching the #11 spot in the Dutch Single Charts. Sia and her band members wore glow-in-the-dark costumes on Jimmy Kimmel Live! in January 2008, performing "Buttons" and "Breathe Me". The Mylo remix of "Breathe Me" was also repeatedly used in their nightly segment "Wall Street Crisis: Is Your Money Safe?" during the economic crisis of 2008-2009.
Sia provides backing vocals on The Bird and the Bee's cover of the Bee Gees's "How Deep is Your Love", which appears on the soundtrack for the Sex and the City film. She also collaborated with Lior on his album, Corner of an Endless Road on the song "I'll Forget You". In August 2008, "Breathe Me" was licensed to Coca-Cola and appeared in their commercial airing during coverage of the 2008 Beijing Olympics. In October 2008, she performed 2 songs on the BBC2 TV show, Later with Jools Holland: "Buttons" and "Soon We'll Be Found". She will appear on Christina Aguilera's forthcoming album, which Sia confirmed on her website's blog to have created four "beautiful" songs and calls Aguilera her "best friend." Sia's song "Breathe Me" is used as the backing music for the Tokyo Games Show trailer of the video game "Prince of Persia" to be published by Ubisoft as well as the movie The Ultimate Gift.
Sia's music video, "Soon We'll Be Found", was featured on the United States front page of the iTunes Music Store. Customers were able to download a high quality version of the video for free. It has garnered overall good reviews from customers, although the average rating as of 10 November 2008 is 3.5 stars.
Her song "I Go to Sleep" was featured on the episode "Gray Hour" on the TV show Dollhouse.
In 2008, Sia talked about her bisexuality in interviews with Scotland on Sunday and AfterEllen.com saying, "I've always been open about it. People are making a fuss of it now because I'm getting successful."
Sia is included on a list of openly gay entertainers in The Advocate's "Forty under 40" issue of June/July 2009.
Christina Aguilera handpicked her to write for her new album Light & Darkness. Currently Sia is in the studio writing with Aguilera. Sia had this to say on the experience thus far: ‘‘We've written some really wonderful songs. I would put any of the songs we've written on one of my albums. And it's a total collaboration. There are some artists who walk in and say ‘I want to write a song about a stiletto', then walk out again. You write the song and they take a third. That's not at all what it's been like working with Christina. Often she saves the day when we're stuck." The collaboration (including Furler's bassist Sam Dixon) already has yielded four tracks.