The world number one also became the first man to win five Roland Garros crowns in succession as the 28-year-old took his record at the tournament to 66 wins against just one defeat.
His tally of 14 majors equals the mark of Pete Sampras and puts him just three behind the all-time record of Roger Federer who is almost five years older.
Defeat was cruel for world number two Djokovic, the 2012 runner-up, who still needs a French Open title to become just the eighth man to complete the career Grand Slam.
"Playing against Novak is always a big challenge, I have lost to him the last four times. Every chance I have to beat him it's because I have had to play to my limit. I feel sorry for Novak. He deserves to win this tournament one day and I am sure he will."
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He added: "It's an amazing, emotional moment for me. I lost the Australian Open final this year when I had a problem with my back. Today tennis has given me back what happened in Australia."
But Nadal, playing in his 20th Grand Slam final to Djokovic's 13th, grew stronger as the final wore on as he ended a four-match losing streak against his old rival.
The 3hr 31min duel ended on a sour note when Djokovic double-faulted on match point, shaken by a shout from the crowd.
"Congratulations to Rafa. To win the French Open nine times is incredible," said Djokovic.
"There's a lot of emotions for me. I gave my maximum with all my strength and force but Rafa was better on the court.