The 44-year-old looked to have killed off his title hopes after running up a quadruple-bogey 8 at the seventh hole on the notoriously-difficult Gary Player-designed course at DLF Golf & Country Club in New Delhi.
However, he regrouped to cover the remaining 11 holes in a brilliant five-under-par for a closing 71 and a nine-under-par 279 total.
After finishing birdie-birdie, Gallacher won by a shot from Japan’s Masahiro Kawamura, with Spaniard Jorge Campillo one further back after a closing 67.
American Julian Suri, the overnight leader, ended up in joint-fourth on six-under after he took an 8 at the par-4 14th when he was three shots clear of the field.
It is Gallacher’s fourth European Tour title triumph but first since he successfully defended the Omega Dubai Desert Classic in 2014, a win that helped him play in the Ryder Cup later that year at Gleneagles.
“I got off to a ropey start and then took 5 off the tee at seven, where I just hit two poor shots, but I stood on the eighth tee and I thought, ‘I am only five behind here’,” he told Sky Sports Golf.
“I was quite calm, to be honest, and I then hit my drive out of the middle and I thought, ‘you know what on this golf course with the weather and the wind swirling, I could stay in touch’.”
Birdies at the ninth, 10th, 11th 12th and 15th helped repair that damage from the seventh and he was tied for the lead with three holes to play.
He then made a solid par at the short 16th, hit a brilliant approach at the 17th then followed a peach of a drive following a lengthy wait on the last tee with an equally impressive iron shot into the par-5 18th.
“I finished it off great,” added Gallacher, smiling. “It was not until I saw the board on 16 that I saw that I was tied for the lead.
“At 16, the wind comes off the right and you’re just trying to get it pin-high to the left, which I did, then my second second into 17 was probably the best shot I’ve for years.
“I was right in between clubs and I just gripped down a little 7-iron and managed to put it to six feet.
“Then my two shots at the last, driver and 4-iron, I just thought to myself that I had played with Matt Wallace last year when he won. I remember what he had done in the play-off and my aim was to do the same as him - and it worked.”
Jack, a mad-keen golfer himself, started caddying for his dad last season and Gallacher admitted it had been a special day having him at his side in the heat of battle.
“It was brilliant having Jack on the bag and he’s great, as well,” he said. “He’s a good caddie. A top lad. He’s quite chilled, so nothing really bothers him.
“Jack just kept saying to me out there, ‘just keep doing what you are doing, make sure you have the right club, get the process right, pick the your shot and hit it - that’s all you can do’. He was as cool as a cucumber. No problem, at all.”
Turning to the camera, Gallacher added: “It is Mother’s Day, as well so I hope my mum (Wilma) back home is enjoying herself!”