The younger Fitzpatrick chased down defending champion Eugenio Chacarra, who led by four strokes overnight and six at one point on the front nine at the DLF Golf and Country Club in Gurugram on Sunday.
Fitzpatrick carded a three-under 69 in the final round to finish nine under for the tournament on 279.
Chacarra slumped to a three-over 75 on Sunday to finish two shots behind at seven under.
Alex's victory followed Matt Fitzpatrick's PGA Tour win at last week's Valspar Championship, making them the first brothers to win in successive weeks on the two tours.
"It can be hard sometimes when you're constantly chasing someone's accolades, but luckily it's my brother so it's not horrific,'' Alex Fitzpatrick said.
"I idolise him, so just trying to be like him in every way. I see my mum and dad tomorrow and we're going to meet my brother in Florida.
"It's been a good few weeks for the Fitzpatricks."
The 27-year-old bogeyed the third and fourth holes on Sunday, but from the moment he birdied the sixth, the chase was on.
Back-to-back gains before the turn took him out in 35, and though he dropped a shot at the 10th, he picked up three in a row from the 11th to move within one.
He took the lead with a birdie on the 15th, where Chacarra made the first of three straight bogeys to effectively surrender his title.
Another birdie at the 17th gave Fitzpatrick a four-stroke lead to take down the last, where he could afford a cautious approach as a double-bogey seven wrapped up a two-shot win.
"I felt like I was playing really nicely, I started to hole some really good putts," he said.
"I just had to ask my caddie how many putts I had (to win) from six feet, so I think that says it all."
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