Bradley took a one-shot lead into the final round at TPC River Highlands and was never in real danger of being caught after making five birdies in his first 12 holes.
The 2011 US PGA Championship winner gave the chasing pack a glimmer of hope with three bogeys in four holes from the 13th, but eventually signed for a closing 68 to finish 23 under par.
Fellow American Zac Blair surged through the field with a final-round 62 to finish 20 under par alongside compatriot Brian Harman, who returned a second consecutive 64.
“This is for all the kids that grew up in New England, who got to sit through the winters and watch other people play golf,” said Bradley, who was born in Vermont, one of the six states which make up the New England region.
“I just am so proud to win this tournament …Â I’m so lucky and thankful to be from this New England area. I just can’t believe it. This seems like a dream.”
World No.1 Scottie Scheffler (65), Patrick Cantlay (67) and Chez Reavie (71) shared fourth place at 19 under, with Rory McIlroy another shot back after a closing 64.
“I got off to a hot start, which was nice and what I felt like I needed,” McIlroy said after a round containing seven birdies and one bogey.
“Then hit a drive on nine that I didn’t think was that bad. Ended up against the boundary fence and made a bogey there which halted the momentum that I had.
“I knew I was never going to win with the way Keegan was playing, but I felt like I probably needed a couple more birdies to finish top five.
“Still, it’s another good week and solid performance after a long run, and looking forward to a couple of weeks off.”
Minwoo Lee carded a final-round three-under-67 to finish as the best Australian at 17 under and in a tie for ninth.
Lucas Herbert (68) at 15 under and Adam Scott (68) one further shot back both finished inside the top 20, with Cameron Davis (63) closing at 11 under and Jason Day (70) nine under.