He graduated in German and Russian (with Serbo-Croatian as a minor) from the Australian National University in Canberra in 1986 (BA). He won a scholarship to read South Slavic studies at the University of Zagreb in the 1988-89 academic year and spent a further postgraduate year at the Pushkin Institute in Moscow in 1989-90. Subsequently he qualified as a translator from Croatian, German, Macedonian and Russian with the National Accreditation Authority for Translators and Interpreters (NAATI) in Australia. Since 1991 he has been living in Germany, where he works as a freelance translator of literature and the humanities. He translates from Russian, Macedonian, and all variants of Serbo-Croatian into English, occasionally into German. In 2005-07 he worked for the International Criminal Tribunal for the former Yugoslavia (ICTY). Since the mid-2000s, Firth has largely been translating works of South Slavic literature. He is a member of the professional associations of translators in the UK (Translators Association) and Germany (VdÜ).