Nadal, chasing a record seventh Roland Garros title, was leading 6-4, 6-3, 2-6, 1-2 when play was halted at 6:50 pm local time (1650 GMT) with conditions on Philippe Chatrier Court becoming increasingly treacherous.
The final, already in progress for three hours, will resume today at 1:00 pm local time (1100 GMT) with Djokovic in the ascendancy and serving for a 3-1 lead in the fourth set.
The last time a French Open men's final failed to be completed on a Sunday was 1973 when it was played on the following Tuesday with Ilie Nastase beating Niki Pilic.
World number one Djokovic, bidding to become only the third man, and first in 43 years, to hold all four Grand Slam titles at the same time had looked down and out at one stage.
After slipping two sets down, he was also a break down at 0-2 in the third before he reeled off eight games in succession to take the third set and lead 2-0 in the fourth.
Nadal had stopped the rot for 2-1 before play was suspended. The Spanish world number two, playing in his 16th Grand Slam final and seeking an 11th major, went into Sunday's final with a staggering record of 51 wins against just one loss at Roland Garros.
Djokovic, the Wimbledon, US Open and Australian Open champion, was looking to emulate Don Budge (1938) and Rod Laver (1962 and 1969) by holding four majors at the same time.