Harrington began refereeing in the Teesside Junior Football Alliance aged 14, after completing a refereeing course whilst at school as part of The Duke of Edinburgh's Award.[2]
After four years as an EFL assistant referee and four years as a National League referee, Harrington was appointed to the EFL Referees List at the start of the 2012–13 season.[3]
Harrington was promoted to a Select Group 2 referee in 2016.[4]
He is the grandson of former Hartlepool United player Tommy McGuigan. McGuigan is in the club's record books for being in the top 10 of the all time top goal scorers list.[9]
Prior to becoming a full-time referee, Harrington worked as a PE teacher at North Shore Academy.[10]