"Down" was written by Ammo, DallasK, Claire Demorest and Radric Davis while its production was handled by Ammo and DallasK. Fifth Harmony recorded "Down" at Westlake Recording Studios in Santa Monica, California. The group started working on their third studio album in January 2017. For the album, they picked up several music producers and contacted those with whom they could collaborate, between them the duo Ammo and DallasK who had produced their biggest success "Work from Home" (2016). Once the track was done, the group had the idea of including the rapper Gucci Mane on it. After listening to the song, he "quickly" created and recorded his verses at Sole Studios in London, England. "Down" was later mixed at Callanwood Fine Arts Center by Phil Tan in Atlanta, Georgia and mastered by Michelle Mancini at Larrebee Studios in North Hollywood.
On May 28, 2017, Fifth Harmony began a daily countdown to the release of "Down" by sharing coordinates of each member's hometown. By going to the specified location, fans were able to decode parts of the song's lyrics through a Snapchat filter. The group shared the single's accompanying cover art on Twitter on May 30, 2017.Epic Records and Syco Music released "Down" to all major streaming services and digital retailers on June 2, 2017, as the lead single from Fifth Harmony's self-titled third studio album. It marked the group's first single as a quartet following original member Camila Cabello's departure, who left in December 2016 to pursue a solo career. In the United States, "Down" was sent to rhythmic contemporary radio stations on June 6 and to contemporary hit radio on June 13, 2017.
The music video premiered on Fifth Harmony's Vevo channel on June 8, 2017. It was directed by James Larese and filmed at the Hollywood Premiere Motel located in the Hollywood Boulevard street in Los Angeles, California. The video opens in the parking lot of a neon-lit motel around night time. Jauregui is in the driver's seat, adjusting her rear-view mirror. Each member steps out of a Dodge Durango. All of them are dressed in retro-style outfits and head towards a room individually. Four doors close simultaneously as the title of the song appears. Jauregui is in a room as dim violet neon lights brightens it as an electric fan circulates air.
The scene is spliced with a scene where the group perform a choreographed dance in the parking lot of the motel with pinkish-violet stage lights in the ground. Jane is wearing a fur-style coat with glasses in her individual take. She sings next to a window where a red neon light streaks through the room. Jauregui is momentarily shown before Kordei's verse is heard. She wears a white and green outfit as she dances sensually through her room in a red setting. The light streaking is normal, compared to the other members. Close-up shots of her face are shown. Brooke then sings, in a bright yellow room. The scene shifts where they perform their dance routine in front of the parking lot, from the start of the video. Gucci Mane takes the next verse, rapping away from the group on the stairs of the motel wearing sunglasses. Quick takes of the group in a pool are also spliced in between. He also raps in front of a wall where four flamingos are seen as the camera pans upwards. They sing together in the pool, where some of them hold on to one another. The video ends with the group standing in front of the parking lot, where the chorus took place.