The 27-year-old English golfer won by a single stroke, holding off top players Will Zalatoris and Scottie Scheffler to finish 6-under par in Sunday's final round of the tournament held in Brookline, Mass.
Fitzpatrick previously won the 2013 U.S. Amateur at the same location, The Country Club. He's the first player from outside the U.S. to win both the U.S. Open and U.S. Amateur.
"No words," Fitzpatrick said after receiving the trophy. "It's what you grow up dreaming of.
It's something I've worked so hard for for such a long time. And you know there was a big monkey on my back trying to win over here.
And everyone, all they ever talked about was that. And you know, to do it as a major for my first win, there's nothing better."Runners-up Zalatoris and Scheffler both finished with a 5-under par.
The tournament took place amid a moment of turmoil in the normally genteel sport. The debut of the controversial Saudi-backed LIV Golf series this month has sowed division in men's professional golf.
LIV Golf, funded by the Saudi Arabia government, has lured top players with huge cash-prize incentives and guaranteed payouts.
In response, the PGA Tour suspended 17 players who chose to compete in the new series.
Despite the tensions hovering over the sport, players on both sides of the divide came together for the Open, which is run by the U.S. Golf Association.
USGA CEO Mike Whan said last week that he could see the possibility that would make it harder for LIV players to compete in future U.S. Opens.