'I am so happy to have won this tournament after having been invited to play,' said Choi. 'To come up with a win is very rewarding. This week the impression of Germany for me is truly wonderful.'
Miguel Angel Jimenez birdied the last to take second place alone at 24-under- par 264. Niclas Fasth and Ian Poulter were one shot further back at 23-under-par 265.
Choi, who enjoyed a breakout season on the PGA Tour last year with two victories and was recently chosen by Gary Player as a captain's pick for the upcoming Presidents Cup, surged into the lead in the third round and held on Sunday to become the first Korean to ever win on the European Tour.
He carried a slim lead over Jimenez into the final round at Golf Club Gut Larchenhof with several other players waiting in the wings for Choi to stumble. Choi struggled with two bogeys on Sunday, but each time he managed to recover in spectacular fashion.
After dropping a shot at the fourth to fall out of the lead, Choi holed out from the fairway for an eagle at the par-4 fifth.
He added a birdie at the seventh but found trouble again with a bogey at the 12th. Choi responded at the par-5 13th when he landed his second shot within 12 feet of the hole. The 33-year-old drained the eagle try to regain the outright lead at 24-under.
Choi then reached the green in two at the par-5 15th and took two putts for a birdie to increase his advantage and capped his victory with a birdie at the 18th.
Jimenez picked up his first birdie of the day at the fourth and hit his approach to eight feet for a birdie at the fifth. The Spaniard birdied the seventh to make the turn at 23-under before dropping a shot with a bogey at the par-3 11th after he missed the green off the tee.
The 39-year-old countered with a birdie at the 13th and tallied a birdie at the last to break the logjam for second place.
'I played very well and I am pleased with my showing the whole week and the whole tournament,' said Jimenez. 'I didn't make any real mistakes today, I just tried my best to catch K.J. but he just beat me in the end and that is golf.'
Darren Clarke, who won this year's WGC-NEC Invitational, completed a 20-under- par 268 performance with a final-round 67. Clarke was joined by Anders Hansen and Carlos Rodiles in a tie for fifth.
Michael Campbell, who won this event in 2000, was one shot further back at 19- under-par 268 along with Mathias Gronberg, David Howell and Jarrod Moseley. Gary Orr finished alone in 12th place at 18-under-par 270.
Lee Westwood had the round of the day with a 63 that included a hole in one at the par-3 eighth.
'As soon as it came off the club it felt pretty good and I said to my caddie that I can't hit it any better than that and it went pretty much straight into the middle of the hole,' said Westwood.
Westwood was joined by Alex Cejka and Henrik Stenson at 17-under-par 271.