He competes in the T37 classification, as he has a mild form of cerebral palsy. His time was a Paralympic record. The medal was later presented to him by his mother, Catherine McKillop, an ambassador of Procter & Gamble.
McKillop has a personal best in his preferred 800 metres of 1:57.22.
He won the 800m title at the 2006 IPC Athletics World Championships, clocking just over 2:02. And he represented Ireland at the 2008 Summer Paralympics, winning a gold medal at the T37 800 m clipping almost three seconds off his previous mark as he strode to an emphatic win in 1:59.41. McKillop won the 800 m title at the 2011 IPC Athletics World Championships in world-record time of 1:58.90, he also set a 1500 m world record but was not awarded a medal because of the lack of entries. In the London 2012 Paralympics, McKillop won gold for the men"s 800 meter t37 with a time of 1:57.22. This was a world record. He won the 1500m T37 race in the 2012 London Paralympics. He is coached by his father Paddy, who was awarded Northern Ireland Sports Coach of the Year. In 2012, McKillop was awarded the The Whang Youn Dai Achievement Award.
