The American finished four shots clear of Hideki Matsuyama
Brooks Koepka's final round of 67 was enough to earn him only his second win on the PGA Tour and a first-ever major championship at the US Open in Erin Hills.
The American finished four shots clear of Japan's Hideki Matsuyama, who also finished runner-up to Koepka in his only other win at the Waste Management Phoenix Open in 2015.
The 27-year-old started well, picking up birdies on his opening two holes, before completing a flawless front nine by picking up another shot on eight.
Around the turn, a bogey on 10 was offset by consecutive birdies on 14, 15 and 16 to hold off a late charge from Matsuyama. The latter shot a final round 66 to keep the heat on Kopeka until the final stretch.
"It's unbelievable, I don't really know what to say," he told Sky Sports. "I felt so confident. All the hard work I put in over the last few months paid off - I'm really happy to see that.
"I was way more confident this week than I've ever been. I don't know what it is. I was striking the ball really well - I was driving the ball onto the fairway, which you need to do out here - and I was putting well."
He admitted the victory was that bit sweeter taking into account how far he had come as a professional.
"For all the hours you put in and to think back about being on the Challenge Tour when four guys are packed into a little car. Then to be a US Open champion? That's pretty cool."
He added: "I look at those and my win on the PGA Tour. I probably haven't won as much as I would have liked, but this will do."
That winning feeling. pic.twitter.com/Lv0VtFDHKP— Brooks Koepka (@BKoepka) June 19, 2017
Ireland's Shane Lowry completed his week with a one-over-par round of 73, to finish on three-over for the tournament.