Terwyn Davies was raised in the Aeron Valley, Ceredigion, and was educated at Felin Fach Primary School and Aberaeron Comprehensive School. He then graduated from the University of Wales Bangor with a degree in Communication, and a post-degree in Journalism. He has been a familiar voice on BBC Radio Cymru since 1999, when he joined the 'Gang Bangor' presenting team and then C2. He presented the C2 and Steve a Terwyn programme three times a week on the station until October 2007. He returned to BBC Radio Cymru in 2010, presenting the nightly Geraint Lloyd programme at different times during the year. Terwyn began his TV career when he joined Telesgop in 2001.

His first job was as a researcher on the Ffermio programme, and then went on to present and produce the Bwletin Ffermio series on S4C until May 2009. He currently works as producer on the Bro series on S4C, and joined the Ffermio reporting team in February 2010, as Daloni Metcalfe took a rest after giving birth to her new son.