Stefan grew up living in a tin shed without electricity in the bush an hour north of Sydney, where he almost died of a red back spider bite when he was nine. His parents were biologists and folk musicians, and he learnt to play guitar and other instruments from an early age. 

He studied pure mathematics at Sydney University, with a particular interest in graph theory and combinatorics, and later studied jazz at the Sydney Conservatorium of Music. He played with the rock band Faker, leading to several ARIA nominations and a platinum single. 

He moved into composing music and sound for theatre, and played live in the landmark production of The War Of The Roses for Sydney Theatre Company, directed by Benedict Andrews, starring Cate Blanchett. He has collaborated with director Simon Stone for almost two decades, working on many highly acclaimed works around the globe, including at the National Theatre, The Young Vic, Burgtheater, Theater Basel, Salzburg Festival, BAM and Park Ave Armoury. His highly acclaimed score for The Glass Menagerie at Belvoir St Theatre, directed by Eamon Flack, was also turned into a ballet. Other notable collaborations include Kip Williams, Anne-Louise Sarks, Pierre Audi, Neil Armfield and Gideon Orbarzanek. He has been commissioned by the Australian Ballet, Opera Queensland and Powerhouse Museum. 

He has won numerous awards for his theatre and film scores, including APRA/AMCOS Screen Music Award for Best Soundtrack Album, a Helpmann Award, Sydney Theatre Awards, OBIE, and he has been nominated for a Dramadesk award, an AACTA award, and was a recipient of a Sidney Myer Creative Fellowship.