The song was released on July 26, 2019 through Columbia Records, as the fourth single from the band's eighth studio album Nine.

It was written by bassist Mark Hoppus, drummer Travis Barker, and guitarist Matt Skiba, as well as producer John Feldmann.

Jacob Neisewander of The Observer described "Darkside", alongside "Pin the Grenade", as the "superior pop-punk jams" on Nine.

[1] Andrew Sacher of BrooklynVegan felt that the song heavily leaned on post-punk.

[2] Mike DeWald of Riff Magazine noted that the song contains "alt-rock and atmospheric aspects".