At the age of 12, Johns and school friends Ben Gillies and Chris Joannou formed a band, originally named "The Innocent Criminals", and practised daily after school for periods of four hours or more. The band's career began when the three members were 15 years old when a demo recording of their song "Tomorrow" won a competition that was run by the SBS TV programme Nomad. The group, now named Silverchair, subsequently accepted a three-album deal from Sony Music in 1994, and the label hurriedly released their first album Frogstomp in 1995 after "Tomorrow" remained in the No. 1 position on the Australian singles chart for six weeks. The band released Freak Show in 1996,followed by Neon Ballroom in 1999 and then Diorama in 2002. Following Diorama, Silverchair embarked on a lengthy hiatus before the release of the next album.
During the post-Diorama hiatus, Johns worked on several side projects, the most notable being The Dissociatives with dance musician/producer Paul Mac. Johns and Mac worked together since Mac's 1997 remix of "Freak" and his contribution to Neon Ballroom. In 2000, they recorded a five-track EP I Can't Believe It's Not Rock. The Dissociatives album was initially recorded in London, United Kingdom, and a few months later, they regrouped in Sydney and Newcastle to finish off the project. The Dissociatives toured with musicians Kim Moyes on drums, Julian Hamilton on keys, and James Haselwood on bass.
In late 2005, Johns and Silverchair reunited and announced the production of the new album entitled Young Modern. The new album was released on 31 March 2007 and was followed by the Across the Great Divide tour with fellow Australian band Powderfinger. In January 2014, Johns co-wrote the song "Impossible" by Australian rapper 360. Johns also sang on the song's chorus. Johns met 360 through Johns' brother Heath, who is also 360's publisher.
For the 40th birthday of the triple j radio station, Beat the Drum, held at Sydney, Australia's Domain on 16 January 2015, Johns performed a piano version of Nirvana's "Smells Like Teen Spirit".
Johns debuted a new song as a solo artist on 29 January 2015 on the Triple J radio station. Titled "Aerial Love", the song is taken from a four-track EP that was released on 13 March 2015. National Music Editor of The Sydney Morning Herald newspaper, Peter Vincent, described the song as "sexy" and "soulful". Johns is expected to release a full-length studio album as a solo artist some time in 2015.In February 2015, "Aerial Love" debuted at No. 50 on the Australian Singles Chart, later peaking at No. 21.
Johns released his fifteen-track debut album as a solo artist on 22 May 2015, entitled Talk. The record features multilayered arrangements of R&B, soul, synthpop, and electronic melodies, all brought to life with Johns' empowering falsetto. Talk peaked at No. 2 on the ARIA Albums Chart in Australia within the first two weeks of its release.The album also achieved some unexpected success in other parts of the world, coming in at No. 1 on the Slovakian iTunes albums chart shortly after release.