Prior to commencing practice, Garth was a classical trumpet player who performed with the Tasmanian, West Australian, Adelaide, Melbourne, and Queensland Symphony Orchestras, in London with the Orchestra of the Age of Enlightenment, and in South East Asia with the Malaysian and Singapore Symphony Orchestras.

Garth appears regularly in the Tasmanian Supreme Court, Federal Court of Australia, Administrative Appeals Tribunal, Magistrates Court of Tasmania as well as providing advice, predominantly in commercial law matters, building and construction, administrative law, industrial law, and disciplinary complaints.