Following the release of Halcyon, Goulding announced that she had plans to repackage the original album, with new songs that focused on electronic music.

For the reissue, Goulding recorded 10 new songs and worked with a variety of producers, including Ryan Tedder, Calvin Harris and Greg Kurstin, to create her desired sound.

In an interview with Elle in July 2013, Goulding announced plans to release a repackaged version of Halcyon with new songs, commenting, "I have such an affinity with electronic music that I can't step away from it.

"[4] Halcyon Days features 10 new tracks, with the first being "Burn", "a celebration of life in its purest form", as described by Idolator's Kathy Iandoli.

[7] "You My Everything" and "Flashlight" (with DJ Fresh) "take Goulding's natural inclination for electronic beats and mix them with the soulful undertone of her vocals", as stated by Iandoli.

[5] "Stay Awake" celebrates "not sleeping and partying all night" over triumphant synth stabs, as highlighted by Frehsee.

"[7] "Under Control" "reclaims empowerment and confidence ('I feel like I'm breathing again'), while wrapped in a mix of fuzzy bass and echoed clanks", as declared by Digital Spy's Lewis Corner.

[7] The second, Alt-J's "Tessellate" loses some of its cryptic airs as Goulding reveals different layers,[8] featuring a "seductive makeover with Chiddy Bang's Xaphoon Jones on the beat.

"[5] Finally, Midnight Star's "Midas Touch" is turned inside out into a fittingly atmospheric declaration of self,[8] having a darker tone.

"[8] Caren Ganz of Rolling Stone praised the album for "confirm[ing] [that] Goulding is doing her best work on clubby tracks with luminescent titles.

"[11] Lewis Corner of Digital Spy opined that the album is "the moment Ellie firmly makes her mark in pop", since its original version "lacked enough upbeat ditties that the wider public seemingly crave.

[27][28] The second single from Halcyon Days, "How Long Will I Love You", was released on 10 November 2013 as the official song for BBC Children in Need 2013 appeal.

[30] In an interview with Capital FM on 9 February 2014, DJ Fresh revealed that he and Goulding had recorded a new version of the song "Flashlight" for single release later in 2014.

[33] The reissue, titled Halcyon Days, was released on 26 August 2013 and contains ten additional tracks, including the lead single "Burn".

[68] This reissue includes the original tracklist in the disc one, meanwhile the Halcyon Days tracks are included in the disco two, as well her soundtracks contributions released during that period of time, such as "Beating Heart" from Divergent, "Mirror" from The Hunger Games: Catching Fire, and "Bittersweet" from The Twilight Saga: Breaking Dawn – Part 2.