Johnston founded the London-based alternative rock band Gallon Drunk in 1990 as frontman and main songwriter.

Johnston was a touring member of Nick Cave and the Bad Seeds in 1994, filling in for Blixa Bargeld during the band's Lollapalooza stint.

[1] He has also recorded and toured with a wide variety of other musicians, including Lydia Lunch (both solo and as the band Big Sexy Noise), French alternative rock group Ulan Bator, Barry Adamson, and as a member of legendary Krautrock band Faust, and recording and performing with PJ Harvey.

On 26 February 2021, Johnston released a collaborative album with musician and photographer Steve Gullick titled We Travel Time.

[2] Johnston's turn to painting initially began with working small scale in hotel rooms on tour, subsequently becoming his primary focus as a daily studio practice.