By September 2013, Sia had been recording vocal tracks at her home studio with the hope of releasing an album the following spring. Her condition for the album was that she would not do any promotions or tours. The only record company interested in the condition was RCA.
In an interview with NME in February 2015, Sia revealed that the album was released a contractual obligation:
Basically, I put this out to get out of my publishing deal. I was planning to be a pop songwriter for other artists. But my publishing deal was as an artist so I had to put one more album out. I didn't want to get famous so I kept all the songs I wanted and had a lot of fun making it.
1000 Forms of Fear is primarily an electropop album, with influences of hip hop and reggae. It opens with "Chandelier", an electropop song that features a reggae-influenced beat. Lyrically, the track talks about "the glitter and fatigue of a party girl's life." The follow-up, "Big Girls Cry", was compared to Alanis Morissette's "Hands Clean". On "Burn the Pages", Furler described a friend she wants to cheer up: "You're twisted up like a slipknot / Tied by a juicehead who just took his T-shot." "Eye of the Needle" is a "military-march" piano ballad, while "Hostage" is a new wave pop and ska track that features Sia's voice "cracking like a punk singer." The sixth song, "Straight for the Knife", is instrumented by strings and lyrically details a tempestuous relationship: "But will someone find me swinging from the rafters / I’m hanging on your every word."
"Fair Game", where Furler sings "Watch me squirm baby, but you're just what I need," is a minimalist and string-laden song about the desire to find an equal partner. The solo version of "Elastic Heart", which originally featured The Weeknd and Diplo, is a trap song. The song addresses "the overwhelming strength [Sia] needed to convince herself that life was worth living after coming out of a crushing relationship." "Free the Animal" lyrically "imagines being killed in lurid, masochistic detail" with the lyrics "Detonate me / Shoot me like a cannon ball / Granulate me / Kill me like an animal." The tenth song, "Fire Meet Gasoline", was compared to Beyoncé's "Halo" by Harriet Gibsone from The Guardian. "Cellophane" is an electropop track, where Furler likens her self to "a basket filled with pain." 1000 Forms of Fear concludes with "Dressed in Black", which Heather Phares of AllMusic described as a ballad "with more depth than the ones she writes for hire."
"Chandelier" served as 1000 Forms of Fear's lead single. It was released for digital download onto the iTunes Stores on 17 March 2014. A music video for the song was released on 6 May 2014; it features dancer Maddie Ziegler in a blonde wig. The single became a commercial success, peaking at number eight on the US Billboard Hot 100, becoming the first single by Furler to appear on the chart as a lead artist. "Chandelier" also peaked within the top five of record charts in Europe and Oceania countries, including: Flanders and France (number one), Australia and Norway (number two), New Zealand (number three), United Kingdom (number six), and Slovakia (number five). The track was certified triple platinum by the Australian Recording Industry Association and gold by Recorded Music NZ.
"Eye of the Needle" was released digitally on 3 June 2014 as a promotional single. while "Big Girls Cry" was made available for music download on 25 June. "Elastic Heart" was released as the fourth single from 1000 Forms of Fear in January 2015. A music video for the song was released on 7 January 2015 and features Ziegler and actor Shia LaBeouf. "Elastic Heart" peaked at number 17 on the US Billboard Hot 100 and charted within the top five charts of several countries, including Australia and Ireland. On 2 April 2015, a music video for "Big Girls Cry" was released. "Fire Meet Gasoline" was officially released as a single in Germany on June 19, 2015.
1000 Forms of Fear received mostly positive reviews from music critics. At Metacritic, which assigns a normalisedrating out of 100 to reviews from mainstream critics, the album received an average score of 76, which indicates "generally favorable reviews", based on 28 reviews. The Boston Globe critic Sarah Rodman described the release as "dynamite," while Heather Phares from AllMusic called the album "the sound of [Sia] owning her success." Writing for The Daily Telegraph, Helen Brown praised the album's production and "inspirational" lyrics showcasing Furler struggling to deal with drug addiction and bipolar disorder. Rolling Stone's Julianne Escobedo Shepherd simply wrote that "she sounds like a superstar;" while Maura Johnston of Spin characterised 1000 Forms of Fear as "a chunk of the human emotional spectrum committed to record." On behalf of The New York Times, Jon Pareles lauded the "loopy, unresolved passions" on the album in favour of "the triumphal, laminated, computer-perfected tone of Sia’s clients."
Writing for Slant Magazine, Annie Galvin opined that 1000 Forms of Fear "should be the vessel that rockets the singer out of relative obscurity and into the stratosphere populated by those more recognizable stars who've come to dominate the pop-music universe thanks, in part, to her songwriting skills." Mikael Wood writing for the Los Angeles Times praised Sia's vocals and the production held by Greg Kurstin. Likewise, Entertainment Weekly's Adam Markovitz positively viewed Sia's voice as "astonishing," giving the album a B score.
On a less enthusiastic review, The Guardian Harriet Gibsone shared that the album was so impeccable and "contemporary-sounding" that "its impact may fade with time." The A.V. Club writer Annie Zaleski wrote: "1000 Forms of Fear certainly has the songs and contemporary sheen to make Sia a star in her own right, but it's at the expense of both her emotional intimacy and her offbeat personality."
Sarah Rodman of The Boston Globe labelled 1000 Forms of Fear the "Best Surprise" of 2014. It ranked number 13 on Digital Spy's list of Top 15 Albums of 2014. Jon Pareles from The New York Times placed the album at number 5 on his list of favourite albums of the year. It also appeared on the lists of the best albums of 2014 of Slant Magazine (number 13) and The Daily Telegraph (number 44). Rolling Stone ranked it number 20 on its list of 20 Best Pop Albums of 2014. At the ARIA Music Awards of 2014, Furler won Album of the Year, Best Female Artist and Best Pop Release for 1000 Forms of Fear. The lead single "Chandelier" received four Grammy nominations for Song of the Year, Record of the Year, Best Pop Solo Performance and Best Music Video at the 57th Grammy Awards.