In 1979, he embarked on studies of classical music with Harold Taylor, John Bache and John Woolfe (Music Director for Stratford's Royal Shakespeare Company) before graduation under the professorship of William Mathias at the University College of North Wales, Bangor.
As a solo guitarist, he commissioned a new guitar sonata from Gareth Glyn and premiered pieces written especially for him by John Pickard, Jochen Eisentraut and Andy Crowdy.
They won two national ensemble competitions and appeared on the BBC's Blue Peter television show, before disbanding in 1997.
In the late 1990s, Tommis joined the experimental band Ogam, which aimed to present traditional Welsh melodies in unusual arrangements.
Since then Tommis has collaborated with musicians such as Huw Warren, Gwyn Evans, and Lleuwen Steffan in the recording of many of his own songs.