The Englishman made four birdies in his final round to sign for a three-under-par 68 and finish on 17 under par, while playing partner Spieth closed with a 66 to force extra holes at Hilton Head Island.
After both players parred the first two play-off holes, Fitzpatrick set up victory by almost holing out from the fairway with a nine iron at the 18th to leave himself with a tap-in birdie while Spieth was unable to hole a 40-foot putt.
The victory is Fitzpatrick’s first since his memorable maiden Major Championship success at last year’s U.S. Open, his ninth worldwide and lifts him to a career-high eighth on the Official World Golf Ranking.
As a child, Fitzpatrick attended the event with his family on holiday and was delighted to land the title and become the first Englishman to win the tournament since Sir Nick Faldo in 1984.
Doesn’t get any better
“It's hard to describe,” Fitzpatrick said of his victory at the designated PGA TOUR event. “I said to Billy, (Foster, his caddie), it doesn't get better than this.
“Walking down here just looking around. It’s a course I dreamed of playing when I was young. I managed to play it a couple of times with my dad. This one means more than anything.”
Ahead of last week’s Masters Tournament, Fitzpatrick said he was in a “rebuild phase” after an injury-hit start to the season but a top ten at Augusta National suggested a return to his best was on the cards.
Fitzpatrick held a one-shot lead over Patrick Cantlay going into the final day after a brilliant eight-under 63 in the third round, with Spieth two shots adrift.
But Spieth made four birdies in his opening six holes to hold a one-shot advantage over Fitzpatrick, who birdied the second and fifth holes before a bogey at the seventh, and Cantlay at the turn.
Fitzpatrick moved into a share of the lead with Spieth on 17 under with birdies on the 15th and 16th, while Cantlay made bogeys at the 13th and 14th to lose ground on his final-round playing partners.
Neither Fitzpatrick or Spieth could find a birdie on the final two holes and the latter was forced to make a tricky downhill six-footer on the 18th green to force the play-off.
Spieth narrowly missed a birdie putt for victory on the first play-off hole, before Fitzpatrick’s stunning approach with a nine iron on the second visit back to the 18th after regulation play proved decisive.
Fitzpatrick will next be in action at this week’s Zurich Classic of New Orleans where he will play alongside his brother and European Challenge Tour member Alex.
“I'm even more excited to go now,” he said.
“That kind of was one of my thoughts going into today, it's a great challenge, a great opportunity to go out and try and win, and fortunately I managed to do that, and then just look forward to next week, and now I can really enjoy next week.”
Masters champion Jon Rahm carded a closing 68 to end the week on 11 under in a share of 15th place along with Tommy Fleetwood and consolidate his position at the top of the FedExCup standings.
DP World Tour