In 2011, at the age of 14, Hemmings began posting YouTube song cover videos, under the username "hemmo1996". Hemmings' first video, a cover of Mike Posner's "Please Don't Go", was posted on 3 February 2011. As Hemmings' covers began gaining traction on the platform, he invited Hood and Clifford to join his videos. The trio eventually added mutual friend Ashton Irwin to their videos, forming the current 5 Seconds of Summer lineup. After months of posting song covers together, the band began attracting interest from major music labels and publishers and signed a publishing deal with Sony/ATV Music Publishing. Hemmings has since released four studio albums with the band, each met with worldwide success: 5 Seconds of Summer (2014), Sounds Good Feels Good (2015), Youngblood (2018), and Calm (2020).