From 2001 Maddison is the bass guitarist of the United States–based grunge band, Mudhoney (which includes Arm), and has worked on their studio albums, Since We've Become Translucent (2002), Under a Billion Suns (2006), The Lucky Ones (2008), Vanishing Point (2013), Digital Garbage (2018) and Plastic Eternity (2023).

[1][2] By 1986 he moved to Sydney, he played bass guitar for noise rock band Lubricated Goat, sometimes under the pseudonym Buster Smallgoods, recording one album, Paddock of Love (July 1988).

[1][2] In 2003 Maddison recalled meeting Stu Spasm (aka Stuart Grey) by chance, "I was crossing the road one day on Cleveland Street ... and Stuart yelled out to me ... he asked me if I was doing anything and if I’d like to play the bass in Lubricated Goat" – they had previously met when Spasm was recording tracks in Perth with an earlier version of Lubricated Goat.

In 1990 Guy Maddison was briefly a member of a studio group, Bushpig, on bass guitar and keyboards, with Tolnay (ex-Bloodloss) and Peter Hill (King Snake Roost) on vocals and harmonica.

[5] This version had formed in Seattle with Mark Arm of Mudhoney on vocals, and Maddison's former bandmates Renestair and Bland.

[5] In 2001, after the departure of founding bass guitarist Matt Lukin, Maddison joined the band Mudhoney, reuniting with Arm.