'I really can't comprehend it at the moment,' said Drummond, who also became the first player to win the Volvo PGA Championship in his first start at the event since Arnold Palmer accomplished the feat in 1975. 'I just got on my game and it is a dream.'
Angel Cabrera, who carried the lead into the final round, shot a 67 to come up two shots short at 17-under-par 271. Joakim Haeggman was one shot further back at 16-under-par 272.
Drummond, a Challenge Tour grad who welcomed in his first child last month, was as close to perfect as you can get Sunday at the Wentworth Club. The Scot, who also celebrated his 30th birthday on Saturday, came into this week ranked 435th in the Official World Golf Rankings and walked away with one of the most prestigious crowns on the European Tour.
While Cabrera and Haeggman battled early on for the lead under rainy conditions on the West Course, Drummond kept pace with a birdie at the par-5 fourth and pulled within one of the top spot with back-to-back birdies starting at the par-4 seventh.
Drummond grabbed a share of the lead with a birdie at the par-3 10th and played his third shot to 4 feet for a birdie at the par-5 12th.
Cabrera persisted, however, and regained a one-stroke advantage with a 9-foot putt for eagle at the very same hole. Drummond then ran home a 40-footer for a birdie at the par-4 13th to regain a share of the lead alongside his Argentine playing partner.
'I played very well, felt very comfortable but Scott was playing very well,' said Cabrera.
Cabrera stumbled with a bogey at the 14th to fall one back putting Drummond in the lead for good. Drummond held off Cabrera with another lengthy birdie putt at the par-5 17th and hit his third shot to the par-5 18th within 7 feet of the hole.
'On the 18th I didn't look at the leaderboard but the cheer from the crowd told me and the look in my caddie's eyes as well,' said Drummond. 'I knew we had done it.'
The Scot converted the birdie try to clinch the biggest victory of his career.
Haeggman, who continued to improve his Ryder Cup standing with another solid performance, moved into the lead early with three consecutive birdies from the third to climb to 14 under.
The Swede's advantage was short-lived and he mixed birdies with bogeys until the closing par-5s. Haeggman tallied a birdie at the 17th and missed the green with his approach to the last.
Haeggman chipped his third to 4 feet and sank the birdie putt to take third place alone after a round of 67.
Hansen, who had the same winning score when he titled by five strokes over Eduardo Romero and Colin Montgomerie in 2002, shot a 64 to join Darren Clarke and Nick Faldo in a tie for fourth place at 15-under-par 273.
Faldo, the 1989 champion at Wentworth, opened with a bogey at the first but countered with birdies at the fourth and later at the seventh.
The legendary English golfer caught fire on the back half and gave the local galleries plenty to cheer for. Faldo ran off three straight birdies starting at the 12th and almost chipped in for an eagle at the 17th.
Faldo tapped in for birdie and closed with a birdie at the last for a round of 66.
First-round leader Ernie Els carded a 68 to finish alone in seventh place at 13-under-par 275. Miguel Angel Jimenez, Thomas Levet and Darren Fichardt followed at 12-under-par 276.
Justin Rose, who held the 36-hole lead, posted his second straight 72 to join Retief Goosen, Adam Scott and Christopher Hanell at 11-under-par 277.