Fells was educated at King Edward VII School, Broomhill, Sheffield, then carried out national service in the British army, before studying at Trinity College, Cambridge where he gained an M.A.
[2] He has been Professor of Energy Conversion at Newcastle University since 1975 and has published some 200 papers on a varied range of topics, including: Fells is a long-standing advocate of nuclear power.
[3] As of 2008, Fells was of the view that "any notion that renewables can provide for all our [energy] requirements is a mischievous and reckless boast".
[8] Fells has made over 500 television and radio programmes, including the TV popular science series Take Nobody's Word For It with Carol Vorderman, and regularly appeared as guest expert and judge on The Great Egg Race from 1979 to 1986.
In 2012 he created a Newcastle-based company, Penultimate Power, to develop small modular reactors.