[1] Duffy refereed the 2009 All-Ireland Senior Football Championship Final between Cork and Kerry at Croke Park.

The decision to appoint Duffy surprised Mick O'Dwyer and Billy Morgan, who thought it would have gone to Pat McEnaney,[2] comments which disappointed former referee Weeshie Fogarty.

[3][needs update] Duffy had done some Sligo and Connacht finals and refereed both the 2009 National Football League opener between Dublin and Tyrone and the 2009 National Football League final between Derry and Kerry.

[1] He also refereed the 2013 National Football League final between Dublin and Tyrone.

[6] He also retired from refereeing, with his last game being the 2017 Connacht Senior Club Football Championship final.