Djokovic will be unveiled as the new No. 1 on Monday when the ATP rankings are released.
Nadal has held the spot for the majority of the season but relinquished the position after withdrawing from the Paris Masters due to injury.
It will be the first time in two years that Djokovic, 31, will lead the rankings.
He said: Reflecting on what Ive been through in the last year, its quite a phenomenal achievement.
Im very, very happy and proud about it. Five months ago, it was highly improbable considering my ranking and the way I played and felt on the court.
Ill probably be able to speak more profoundly about it when the season is done and hopefully if I get to finish as No. 1.
While delighted to return to the top of the sport, Djokovic said he was unable to be too ecstatic while the race to end the year as world No. 1 was still on.
Though it appears unlikely, Nadal or Roger Federer could take the spot from Djokovic before the season ends.
Its not the end of the season, Djokovic added. Rafa obviously is struggling with injuries since the US Open. But the race is still there.
Roger is in the race. Rafa is in the race. It depends who is going to play the ATP Finals in London. So as I said, I cant be too ecstatic about it.
Wimbledon and US Open champion Djokovic is currently playing at the Paris Masters and cruised through to the quarter-finals, where he will meet Marin Cilic.