Growing up in Newcastle, Australia, he formed Silverchair at the age of 14. Johns has found it somewhat difficult to cope with the fame brought on, at one stage suffering from anorexia nervosa and depression.
By 2002, Johns appeared to have recovered from his internal trauma and was ready for the release of what he regarded as his band's masterpiece, Diorama. However, just as the album was due for release Johns was struck down with severe arthritis and spent most of 2002 unable to perform. It was feared that he may not be able to perform for years, and perhaps would never play again.
Still unable to play for extended periods, he performed again in October 2002 at the ARIA awards ceremony. His recovery has proceeded and Silverchair (as of February 2003) performing an extended Australian concert tour.
Johns has also done the side project The Dissociatives (a.k.a. I Can't Believe It's Not Rock!) with dance musician Paul Mac.