Brown fired a 5-under 67 in the final round to finish at 18-under 270, three strokes clear of the field.
The 33-year-old, whose only previous title came in the Asia Tours SAIL Open last week, made four straight birdies'from the 12th to 15th holes'to surge past Japans Taichiro Kiyota.
Overnight leader Kiyota, looking for his first title, carded two bogies over the last eight holes to slide into a three-way tie for second at 15-under 273, along with Australians Greg Chalmers and Scott Strange.
Brown returned to professional golf in 2006 following a three-year break. Disenchanted at his performance in his previous stint, Brown quit golf and took up an office job, but eventually returned to the game.
This is incredible. Its amazing to have my name there on the Johnnie Walker Classic, he said. Ive worked extremely hard for this. Its a dream come true.
I wasnt good enough physically and mentally the first time round and worked extremely hard during the past year and a half.
Brown described his two victories on two different courses on the outskirts of New Delhi as a blur.
After last week, I thought I would have a shot at the title if I played solid again, Brown said. I dont think I hit a fairway or green getting to the 10th. Then I said to myself, Lets have a solid nine holes, and the birdies started falling. The rest is a dream.
The Johnnie Walker Classic is a $2.5 million event jointly sanctioned by the European and Asian Tours. The title also secured Brown an exemption to play on the European Tour until the end of 2010.
Kiyota said he paid the penalty for contemplating the winners check over the last nine holes.
As the score shows, the front nine were great but I started to think about victory on the back nine and lost my pace, he said. On the 12th hole, I began thinking that I could win and made a bogey. That just knocked me off my pace, but Mark played great golf over the back nine.
Swedens Johan Edfors fired the best final round, a 7-under 65 for a total of 14-under 274, which placed him in a tie for fifth with Indian Shiv Kapur and Graeme Storm of England.