After switching from guitar, Rosser started playing drums when he was eleven years old. Rosser's first gig was with high school punk band called "The Warthogs" who covered The Clash, The Ramones and the Sex Pistols. Since then he has performed and recorded with many bands including Bigphallica, Enemy Me, Zahlu, The City Lights, Sixties Mania, Infusion, Art vs Science, Wolfmother and most recently The Cracks. He also performed in a super group featuring Phil Jamieson, Chris Cheney, Brad Shepherd, and Ian Rilen.
Rosser toured the world with Sixties Mania, an Aussie 60s music cover band, before joining The Vines. Rosser auditioned after answering an ad which the band had placed. He was asked to join to replace The Vines previous drummer, David Oliffe.
Under the pseudonym "Hemi-Roid", Rosser also performs as the drummer with a hair metal cover band called "BigPhallica".
When The Vines former drummer David Oliffe left the band while recording "Highly Evolved", Craig Nicholls and Patrick Matthews placed an ad in an Australian newspaper for a drummer who was an experienced live performer. Rosser auditioned for Nicholls and Matthews and was chosen to be the new Vines drummer. Rosser continued to play with the band as it toured in support Melodia and Future Primitive. He left the Vines, along with guitarist Ryan Griffiths, in December 2011.
Hamish brews beer and has launched a beer called Skinny Blonde. The beer won the Peoples Choice awards at the 2008 Australian Beer Festival held at the Rocks in Sydney.
In June 2009, Skinny Blonde attracted national controversy across Australia over its beer bottle packaging which, through the use of modern ink technology, has a 1950s style pin up girl called 'Daisy' on the beer bottle label, slowly revealing herself as the beer level drops and the bottle temperature rises. This angered feminists who claimed "This is another blatant example of the alcohol industry objectifying women to move product". Hamish responded, "This generation of Aussies have grown up on the beach and topless girls in bikinis are commonplace. The label and website is in no way meant to offend women or anyone else, rather embrace the Australian beach culture." He was also quoted as saying that the beer was "just a bit of cheeky fun."