The American entered the day three shots clear of Matt Kuchar but found himself a shot behind his countryman with five holes to play on a remarkable afternoon at Royal Birkdale.
A stunning birdie-eagle-birdie-birdie run followed that saw him sign for a 69 and a 12 under par total that gave him a three-shot victory over his playing partner who also recorded a 69.
China’s Li Haotong was then at six under, a shot clear of World Number Four Rory McIlroy and Spaniard Rafa Cabrera Bello, with South African Branden Grace, Swede Alex Noren, England’s Matthew Southgate, US Open champion Brooks Koepka and Australian Marc Leishman at four under.
Spieth lost a three-shot lead over the course of 13 holes before playing his final five holes in 5 under to rally past Matt Kuchar, win his 11th TOUR title and take the FedExCup lead.
Spieth used a remarkable string of holes on the back nine to hold off Matt Kuchar and win the third major championship of his career. He won by three shots — the same margin he started the day with — after a final round 1-under-69.
He played the last five holes in 5-under-par.
Spieth was behind by a shot after 13 holes when he went birdie-eagle-birdie-birdie to snatch the tournament away from Kuchar. The sizzling stretch of play came after he made an improbable bogey from the driving range after taking an unplayable penalty shot.
After winning the Masters Tournament and US Open in 2015, Spieth has now been crowned Champion Golfer of the Year for the first time and is just one step away from the career grand slam.
For Kuchar – Bronze Medal winner at the Olympic Men’s Golf Competition – it was a best finish at a Major and a ninth top ten in golf’s four biggest events.
Spieth’s lead was very quickly cut to one shot as he got in trouble off the tee to bogey the first and Kuchar hit a stunning iron into tap-in range at the second for a birdie.
Kuchar found the sand with his second shot on the third to give back the shot he had just picked up but Spieth gave him a reprieve when missed a short one and failed to get up and down from over the back of the green.
Spieth’s shaky start continued as he three-putted the fourth to drop another shot and with Kuchar getting up and down from the bunker at the front of the green, there was a tie for the lead.
Despite a poor tee-shot, Spieth hit an excellent second to register a birdie on the fifth and when Kuchar failed to get up and down from a bunker on the next, the lead was back to two shots.
The roller coaster ride continued, though, and Kuchar birdied the ninth with Spieth three-putting again to make it a tie at the top.
A trio of pars were then shared but Spieth went a long way right off the tee on the 13th and it took almost 15 minutes as he took an unplayable lie, played his third from the practice area and somehow dropped only one shot.
That gave Kuchar the lead but Spieth was inches from holing his tee-shot on the next and the resulting birdie meant the two were level again.
Spieth had his tail up now and after hitting the 15th green in two he holed a 35-footer for eagle. Kuchar made a birdie to limit the damage but Spieth birdied the next from distance and remarkably he was two ahead and back to where he started the day at 11 under.
Kuchar closed with a bogey up the last as Spieth claimed an ultimately convincing victory.
Grace had fired the first 62 in Major history on Saturday and when Li hit a stunning approach to the 18th for a fourth consecutive birdie, he became the 32nd man to shoot a 63. He also had gains on the eighth, ninth and 12th in a bogey-free effort.
McIlroy birdied the ninth and 11th but bogeyed the 15th before an eagle on the 17th gave him some brief hopes which were extinguished by a par on the last.
Cabrera Bello birdied the eighth but gave the shot back on the 11th before making gains on the 12th and 17th.
Southgate finished in a tie for 12th at Royal Troon last year and improved on that thanks to a closing 65 containing six birdies, while Noren had four birdies in a 67.
Grace will never forget his week at Birkdale and he closed with a level par 72, with Leishman singing for a 65 and Koepka a 71.