After a five-decade-long career, Juergen Hasenkopf, 73, says he can continue to travel around the world for 10 more years
The win in Buriram gives him an insurmountable lead over closest rival Andrea Dovizioso with four races left in the season.
Spain's Marquez finished in 39min 36.223sec, just ahead of 20-year-old rookie Frenchman Quartararo with another Spaniard Maverick Vinales third.
With six premier-class titles, the 26-year-old Honda superstar now pushes past Australian legend Mick Doohan.
He trails only Italian great Valentino Rossi, who won the last of his seven championships in 2009, and Giacomo Agostini, whose record eighth came in 1975.
Marquez jumped up and down with joy after the victory and was handed a large pool-style 'eight-ball' to signify the eight overall championships across all classes he has won.
Starting from third on the grid, Honda's Marquez quickly slipped by Vinales and spent most of the race trying to overcome Quartararo on a Yamaha who led from pole position.
Quartararo held the lead through 25 of the 26 laps but Marquez made his move on the final circuit, flying past the leader as the crowd screamed in delight.
Marquez told reporters that it was now "time to enjoy it" after a high-pressure season with many competitors clamouring to topple the reigning champion.
"Everybody is looking to beat you, it's not easy," a relieved-looking Marquez said after his fourth consecutive MotoGP title.
He also described the 2019 season as his best ever in MotoGP.
However, he insisted that winning a seventh world title in the elite class in 2020 would prove an even tougher challenge.
"It will be difficult to do better next year," said Marquez who has nine wins in 15 races so far this season.
Referring to the 2014 season in which he won 13 times, including 10 in a row, Marquez said he feels that the competitive level of the championship has tightened.
"If you look at my lead in terms of points, you're going to say it was an easy year but, believe me, facing the pressure and the fact that everyone wants to win and beat you, it's not easy."
Marquez now has 325 points this season with Dovizioso, who was fourth Sunday, on 215.
In 2020, the champion sees Quartararo becoming a major threat.
"Fabio is getting stronger every time and he will be a serious rival for the championship," said the Spaniard.
"His style reminds me of (current Honda teammate) Jorge Lorenzo when he was at his best with Yamaha. He uses the whole track and manages his race very well."
Quartararo admitted that he was "really frustrated" at losing in such a close fight to the finish but recognised that it was a great result considering who he was up against.
"We tried until the last corner," the 20-year-old said.
Marquez went into the race with such a comfortable lead that he did not necessarily need to finish first to clinch the championship.
The stunning performance in Buriram, a rural town in northeastern Thailand that has banked its development on sports infrastructure, also came after Marquez crashed hard in practice on Friday and had to go to hospital.
But the fierce competitor was declared fit to race and rebounded to finish third in qualifying.
Marquez won the inaugural race in Buriram last year in another last-corner thriller against Dovizioso.
Clear skies prevailed after a downpour soaked the track on Saturday, delaying start times and creating slippery conditions for riders.
Italy's Luca Marini won the Moto2 while Albert Arenas from Spain grabbed the Moto3 victory.
After a five-decade-long career, Juergen Hasenkopf, 73, says he can continue to travel around the world for 10 more years
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