In an enthralling final round, the 28-year-old Haddington-based player closed with a six-under-par 66 for a 24-under 264 total to become the first Scottish player to win on home soil on the circuit since Paul Lawrie in 2012.
He held off Englishman James Morrison, who closed with a 63 to finish second, with Spaniard Santiago Tarrio (68) finishing third on 21-under.
In a great week for the Caledonian contingent, David Law (68) and Calum Hill (70) ended up a shot further back in a share of fourth spot.
“So many emotions,” admitted Forrest of his first victory as a professional in an interview with Sky Sports Golf. “To do it in front of everyone who has come up to support me, the last year and a half having been a real challenge on and off the course, I’m delighted, it’ll take a while to sink in.”
On his fantastic finish, the former Scottish Amateur champion said: “I saw the scoreboard and knew what I needed to do. I hit a great nine iron into 17, nice and close, that really helps. And two great shots into 18, it was a great way to finish.”
The win, which was worth around £160,000 and saw him jump 56 spots to 33rd in the Race to Dubai standings, was the first on home turf by a Scot since Lawrie landed the Johnnie Walker Championship at Gleneagles nine years ago.
“It means so much,” admitted Forrest. “We’ve been through quite a lot as a family. To do it here, it’s what I’ve always dreamed of, winning a European Tour event. I can’t believe it. There’s a big party at the in-laws tonight, so we’ll look forward to that.”
Livingston-born Forrest was introduced to golf by his dad when the family lived in West Lothian and he has been his driving force since losing a battle with cancer in 2012.
“Losing my dad was a big change in our lives,” said Forrest, who was warmly hugged by his mum Audrey, sister Alisa and girlfriend Christy Farrell as he made his way off the 18th green.
“It’s not an easy thing to deal with and we’ve all dealt with it in different ways. I think I’ve just put a lot into golf, put a lot of my focus into golf.
“I wish he was here to see this, he’d be so chuffed. He’s been the big inspiration and a lot of the reason why I’ve really knuckled down and kept going when times were tough.”
Starting out in a share of the lead with Hill after carding a brilliant 62 on Saturday, Forrest bogeyed the second after missing the green on the left but was quickly back into his stride again with back-to-back birdies at the next two holes.
He also picked up a shot at the par-5 sixth but, with Hill, who had already birdied the third and fifth, walked in a 16-foot eagle putt at the same hole to open up a two-shot lead over his compatriot as it looked to have turned into a two-horse race.
After Hill then missed a good birdie chance at the par-4 seventh, Forrest hit a brilliant tee shot to three feet for a birdie-2 at the next before Hill then dropped only his third shot of the week with a three-putt from no more than 15 feet at the ninth.
That left them sharing the lead, but not for long. Perhaps a bit rattled, Hill was left off the tee at the par-4 10th then found a gorse bush on the right with his next one, leading to a penalty drop and a double-bogey 6.
Set up by a huge drive, Forrest made a birdie there for a three-shot swing, his lead becoming four shots as he followed that by making another 2 from close range at the 11th but only briefly as Law and Morrison went on back-nine birdie runs.
Law, who was bidding to add to his breakthrough win in the ISPS Handa Vic Open in 2019, made three gains in a row from the 11th, with Morrison making his move with five straight gains from the same starting point.
The Englishman, who was attempting to land a third tour win, hit his approach stiff at the 13th then rolled in a 20-footer at the next before capping the brilliant burst by converting from five feet at the par-4 15th.
Around the same time that run eventually ended, Forrest made a “huge” par save at the 14th, where he found a nasty spot through the back of the green but salvaged the situation by keeping his cool to hole a 12-footer.
Hill had got back on track with a fine birdie at the par-5 12th, with Law also hanging in until dropping his first shot since the 11th in Thursday’s opening circuit with an untimely three-putt bogey at the 16th.
Forrest suffered the same fate there, dropping him into a tie for the lead with Morrison, who then got his nose in front with a closing birdie, coaxing in a 10-foot downhill putt to cap a stunning last-day effort.
That left Forrest needing a big finish and he was up to the task. As had been the case at the eighth and 11th, his tee shot at the par-3 17th was exceptional, setting up another three-footer for a birdie.
“We had three really good numbers, it sometimes just works like that,” he said of those trio of 2s later. “It sometimes just works like that. I hit three cracking shots within ten feet in total. It’s always nice when you can knock them in really close.”
With the pressure on, he then hit two fine shots - his approach from around 260 yards was a majestic 2-iron - to find the back edge at the last and it was job done as he two-putted from around 20 feet.
“It hasn’t sunk in yet. I’m sure it will,” said Forrest, who is the 26th Scot to win on the European Tour and first since his Bounce Sport stablemate, Bob MacIntyre, made his breakthrough in Cyprus last November.