Having struggled for form and with injuries, Koepka made the controversial decision to move to LIV Golf last year, the general consensus being that the American may not rediscover his previous ruthlessness.
However, after squandering an opportunity to win the Masters last month, Koepka made no such mistake on Sunday in New York, countering four bogeys with seven birdies to see off the challenge of Viktor Hovland.
Koepka led throughout the final day, a result of birdies on two, three and four, and it enabled him to make mistakes in his search for a third US PGA crown.
The defining moment came on the 16th hole, Hovland hitting a shot into the lip of the bunker which led to a double-bogey, enabling Koepka to move four shots ahead with two to play.
To Hovland's credit, a birdie on the last helped halved that deficit, leading to a share of second with Scottie Scheffler, but Koepka played a perfect final hole to arguably seal the greatest moment of his career.
While another place of history awaits Koepka, the day belonged to PGA professional Michael Block, who hit a slam-dunk hole-in-one on the 15th hole.
The 46-year-old, who has only ever played 24 PGA Tour events and missed the cut in six majors, achieved the feat in the knowledge that he required a top-15 finish to qualify for next year's tournament.
Block, who played alongside Rory McIlroy, then produced a sensational up-and-down on the last to earn a share of 15th, the American later revealing that he did not look at a leaderboard all day and had no idea of the consequences of his final eight-foot putt.