The 27-year old from Florida sealed the victory with a run of three consecutive birdies starting on the 14th hole that saw him pull away from nearest challenger Brian Harman over the final stretch to win by four shots.
Koepka’s win means that the last seven majors have all been won by first-time winners.
He started the day in the best possible way, birdieing the first two holes, and picked up another at the eighth as he went out in 33.
A bogey at 10 saw him drop a shot, but the turning point came at the 13th when he saved par on the short 13th with a tricky 10-footer after missing the green.
Koepka then pulled away from the field and effectively sealed the win with a run of three birdies starting at the par-five 14th.
A fifteen foot birdie putt at the 15th and another one at the 16th saw him stretch his lead to four shots with just two to play as he parred the final two holes to secure the win and tie Rory McIlroy’s 2011 record at Congressional for the lowest ever US Open total of 16-under par.
Harman, who had taken the outright lead earlier in the round with a birdie at three, seemed to fade as the pressure increased, bogeying the 12th after finding the rough and missing a short putt on the 13th hole as Koepka was going the other way.
He rallied with birdies at 14 and 16, but bogeyed the final hole after finding a bunker off the tee to slip to 12-under and a tie for second with Hideki Matsuyama of Japan.
Matsuyama shot an eight birdie, two bogey round of 66, while England’s Tommy Fleetwood shot an even par round of 72 to finish in fourth spot to come in at 11-under.
Rickie Fowler, who had looked like he could finally break his major duck, shot a disappointing final round of 72 to finish in a tie for fifth place along with compatriots Xander Schauffele (69) and Bill Haas (69).