Dunnion is the son of Danny and Marian Dunnion and came from a family of three, including his brother Donal and sister Donna.[3][4] His sister Donna Boyle (wife of Brendan Boyle) also played for Four Masters but died following an illness at the age of 41 in February 2022.[3][4] Dunnion is a brother-in-law of Karl Lacey.[5]
Dunnion was first called up to the senior team by Brian McEniff for winter training in 2003.[7] He played in the 2006 Ulster Senior Football Championship Final at Croke Park and scored one point.[8]
Nominated for an All Star award in 2006, he later became hampered by injury which caused him to miss Donegal's 2011 Ulster Senior Football Championship success.[2] A member of the Donegal team that won the National Football League in 2007, playing from the start to the end in the final against Mayo,[9] His injury nightmare began during the 2007 Ulster Senior Football Championship. Having played all the way through the league, including the final won by Donegal, as well as the Ulster Senior Football Championship quarter-final against Armagh, he tore his groin kicking a ball while running out at Clones for the semi-final against Tyrone. In the following years he underwent four major operations, three on the groin and one on the posterior cruciate he ruptured while playing for his club.[10]
^ abCraig, Frank (7 July 2022). "Donna Dunnion Boyle Memorial Cup unveiled". Donegal News. p. 70. Donna sadly passed away last February following a long but brave battle with illness. However the 41-year-old wife, teacher and mum of two has left a lasting legacy — one that will now be honoured by the renaming of the top LGFA trophy in the county… Donna's husband Brendan, father Danny and brother Barry attended Tuesday night's draw… Donna's husband Brendan — a former Ardara and Donegal star — thanked the county LGFA for the gesture.
^McNulty, Chris (27 July 2012). "'Baby Give It Up' for the Ulster champions". Donegal News. Retrieved 27 July 2012. Dunnion hasn't competitively under Jim McGuinness since the opening National League game of 2011 against Sligo – but the Four Masters man is regarded as a key member of the group.