Gethin has been working in the television and film industry since the early 80s. He was a co-founder of successful Welsh production companies Criw Byw and Boda before joining the BBC as an Executive Producer in 2001. After leaving the BBC in 2006 he worked as a freelance producer and director developing and producing music and drama projects for a number of independent companies as well as the BBC. From 2011 to 2016 he was producer of the first two series of international hit detective drama Hinterland/Y Gwyll (BBC4/S4C/A3M International). In 2017 he produced The Miniaturist (BBC1/ WGBH) a two part adaptation of the eponymous best selling novel by Jessie Burton. Gethin was acting commissioning editor for drama at S4C from May 2017 to May 2018, where he was Executive Producer on Keeping Faith (S4C/BBC), Bang! (S4C/BBC) and Hidden (S4C/BBC4). He joined Triongl in July 2018.