Downie studied music at York University. He then completed his MA in composition and analysis at the University of Durham, where he worked extensively on computer music composition.  This period culminated in attendance at the Centre Acanthes workshops with Boulez  in Avignon, and research at the Institut de Recherche et coordination acoustique/musique (IRCAM) Paris, both supported by study grants from the Ralph Vaughan Williams Trust.  He then completed research in artificial intelligence and music in the Department of Computer Science, Cardiff University and gained a PhD in Computer Science in 1994.

Since this time, Downie's music has been exclusively instrumental in focus, though it continues to be informed by his earlier researches into the formal specification of  creative processes.  He made his London debut at the Queen Elizabeth Hall in the performance of his Ground State for ensemble and electronics.  Subsequently his music has been featured in festivals in continental Europe including Nuovi Spazi Musicali, Nuova Consonanza, Musica Scienza, and the Saarbrucken Festival. And his music has been broadcast on German and Italian radio.  In 1994 he was an invited composer at the Darmstadt Summer School.  He is published by Editio Musica Budapest.  In addition, his music is regularly performed on BBC Radio Three, a full profile of his music having been featured on Hear and Now in May 2001.  He has recently  completed his BBC orchestral commission, forms 6: event aggregates, which will be premiered by the BBC National Orchestra of Wales in 2006.  Downie is artistic director of the Contemporary Music Ensemble of Wales, which regularly records for BBC R3.  His critical writings have been published in several sources including Perspectives of New Music.

Downie is  senior lecturer in computer science in the Faculty of Computing, Engineering, and Mathematical Sciences at the University of the West of England, Bristol, where he leads programmes in AI, programming, and object orientation and where he pursues research into the algorithmic formalisation of music composition.