[3][5] Harrington took part in the 2012 and 2013 Snowdonia Marathon alongside his friend and fellow actor Mark Lewis Jones.
He has also had roles in Coronation Street, Spooks, Casualty, Holby City, Hustle, Dalziel and Pascoe, Silent Witness, Lark Rise to Candleford, and Poldark.
He won a BAFTA Cymru Award for his portrayal of a young gay hustler in the BBC film Dafydd, part of the Wales Playhouse programme.
[9] On stage, Harrington has toured with Fiction Factory/Y Cwmni's productions of Ed Thomas's plays House of America, Gas Station Angel and Stone City Blue.
In 2015, Harrington won another BAFTA Cymru Award for his role as DCI Tom Matthias in Y Gwyll / Hinterland.