Nadal also did not win the title in 2016, as he withdrew with an injury before his third-round match.
If there were any reason for a bit of intrigue entering Sunday's match, it was this: Thiem beat Nadal in two sets on red clay at Rome in May 2017 and again at Madrid last month.
Against seventh seed Thiem he was at his destructive best, using his athleticism and mental resilience to wear the Austrian down with his relentless shot-making.
"That's my biggest goal, to get into the next one and then to do it better than today", he said.
Rafael Nadal once again proved why he is called the King of Clay as he extended his record at the French Open on Sunday. Not much more of a daunting task than doing so against Nadal at the French Open, where he is now 11-0 in finals and 86-2 overall.
With Novak Djokovic far from his best and Andy Murray still a question mark after hip surgery, per Kevin Mitchell of the Guardian, the route for the likes of Federer and Nadal is about as clear as they could hope.
"If you tell me seven, eight years ago that I will be here. having this trophy with me again, I will tell you that is something nearly impossible", Nadal said.
An edgy Thiem won only one of the first eight points as Nadal, cheered to the rafters when he walked on court, bristled with intent. In the fourth game of the third set, he had the physio attend to his left hand because a finger cramp was making it hard for him to grip the racquet.
'Of course I would love to have 20 like Roger in the future or even more, but being honest, is something that is not in my mind. Thiem, 24, is the only player to beat Nadal on clay in the past two years.
The 31-year-old now holds 17 Grand Slam titles, just three behind Roger Federer. Nadal's had some challenges at Roland-Garros' championship stage over the years, but few athletes in any sport have ever been more acclimatized to a venue the way Nadal has owned the terra firma of Roland-Garros' grounds.
We picked up a victor in Friday's semi-final with Rafa Nadal comprehensively thrashing Juan Martin Del Potro, to cover the -6.5 game handicap easily. Serving to stay in the set at 4-5, the Austrian had Nadal scampering with a massive forehand down the line, but with the entire expanse of the court to play with, he dumped a resultant backhand volley into the net. Now, six Slams later, Federer still keeps his lead at three. Thiem was not easily cowed down by the Nadal forehand, nor the Popeye-bicep it finished off on.
The number of Masters 1000 titles won by Nadal, the most by a single player since the series began in 1990.