He began piano lessons at the age of four and later attended King's College School, Wimbledon, by which time he was also learning viola, violin and orchestral percussion.
After leaving Cambridge, Powell's first professional engagement was as a soloist at the BBC Proms, London in August 1970, playing Terry Riley's Keyboard Studies with Roger Smalley.
He also began to serve as a session player, and founded the group "Come to the Edge" with Robin Thompson and Morris Pert, which performed regularly with the Japanese percussion virtuoso Stomu Yamashta.
Living Stones received its world première at St Davids Cathedral, Wales, on 27 October 2007, and Glasiad y dydd dros Ben Dinas at the City of London Festival on 19 March 2008.
In 2017, after a break from film scoring of nearly 30 years, he composed original music for the sci-fi short Here We Go Again, Rubinot!, directed by Italian cinematographer Giuliano Tomassacci.