It was written by Sigala, Faith, Jess Glynne, Jin Jin, Josh Record, Andrew Bullimore and Joakim Jarl with the song's production handled by Sigala, Joe Ashworth and Jarly.

"Lullaby" is included on the Zeitgeist Edition of Faith's fourth studio album, The Architect.

On 12 January 2019, "Lullaby" was nominated for Best British Single at the Brit Awards.

"Lullaby" was first announced by Sigala on 22 February 2018, it is Faith's second dance collaboration after "Changing" with Sigma in 2014.

Talking about the song, Sigala said: "'Lullaby' is about always going back to that person who has stuck with you through all the highs and the lows.