The 22-year-old beat the opposition to claim the most convincing of victories in the 1500m - T37.
He had a season's best coming into the race more than 20 seconds faster than the next quickest runner in the field and it proved as comprehensive on the track as it looked on paper.
Content to sit behind Australia's Brad Scott early on, McKillop passed him before stretching clear from way out, already acknowledging the applause of the crowd as he came off the final bend.
His time of 4:08.11 was a new Paralympic Games record and more than six seconds ahead of silver-winner Scott. Tunisia's Mohamed Charmi took bronze.
McKillop said: 'When (team-mate) Jason (Smyth) won two gold medals (in 2008) I was quite envious because he had the chance of it.
'I only won the gold in the 800m and I came back thinking I wish there was a 1500m because that's my preferred discipline on the track.
'So when I was notified there was going to be two races (at London 2012) I was licking my lips ready to train even harder to go and win the double.'
Elsewhere, 18-year-old USA athlete Raymond Martin also made it double gold with victory in the 400m - T52 to add to his 100m crown.
Martin was a class apart as he came home in 58.54, almost two seconds ahead of silver medallist Tomoya Ito of Japan, with Austria's Thomas Geierspichler getting the bronze.
Poland's Karolina Kucharczyk jumped a world record 6.00m to take the Long Jump - F20 crown, becoming the first woman to hit the six-metre barrier.
It was an incredible series from the Pole, who extended the record with her first, second, third and then fifth jumps.
Moroccan El Amin Chentouf smashed the 5000m - T12 world record to take gold in 13:53.76, with the top four all coming home within the previous mark of 14:24.02.
Kenya's Samwel Mushai Kimani became the first man to dip under four minutes as he set a world record 3:58.37 in the 1500m - T11.
Elsewhere, Cuba's Omara Durand won the 400m - T13 and Germany's Birgit Kober won the Javelin - F33/34/52/53.
Finland's Toni Piispanen lowered the Paralympic Games 100m - T51 record to 21.72 to take gold.
Mickey Bushell delighted the Great Britain by winning the 100m - T53, while Tunisia's Mohamed Farhat Chida won the 400m - T38, Fiji's Iliesa Delana won the High Jump - F42 and USA athlete Tatyana McFadden the 400m - T54.
Other gold medallists today included China's Yao Juan in the women's Shot Put - F42/44 and compatriot Liu Fuliang in the Long Jump - F46, Ukraine's Andrii Holivets in the Shot Put - F11/12 and Germany's Sebastian Ernst Klaus Dietz in the Discus - F35/36.