The Spaniard, chasing a record-extending 13th triumph at Roland Garros, will meet the world number one for the seventh time at Roland Garros, having beaten him six times out of seven, including twice in the two finals they played.
The 34-year-old Nadal, now undefeated in 13 French Open semi-finals, once again relied on his massive forehand to notch up his 10th win in 11 encounters with Schwartzman, who beat him at the Italian Open last month.
Nadal, who advanced into the Paris final without dropping a set for the first time since 2017, will equal Roger Federer's men's singles record of winning 20 majors if he triumphs in the final.
Schwartzman, the 12th seed, kept Nadal on court for over three hours but managed only 24 winners in the contest.
"With these conditions it's very difficult, and it's still incredible to be in the final again. Thanks to my team, my family. It's a beautiful moment for me," said Nadal, who has now progressed to the final without losing a set for the sixth time.
"I know with Diego it's very difficult until the end. He's one of the players who makes more (service) breaks on the tour.
"A few weeks ago, I lost in Rome so I expected a very tough match. Happy the way that I played. I think I have been improving and today has been a very positive match for me."
Djokovic defended resolutely to outlast big-hitting Greek Stefanos Tsitsipas 6-3 6-2 5-7 4-6 6-1 in an enthralling contest.
The Serb, whose 2016 Roland Garros triumph features among his 17 major titles, had a match point in the third set but saw the 22-year-old Tsitsipas fight back spectacularly to level the match at two sets apiece.
Tsitsipas, seeded fifth, ran out of steam in the deciding set but saved another match point before the 33-year-old sealed the win with a crushing service return in three hours and 54 minutes on Court Philippe Chatrier.
"Here, he (Nadal) is the favourite, it's his home here. With all the titles he's won ... but in 2015 I won here against him in the quarter-finals," Djokovic said in his on-court interview.
"I hope I can recuperate, I need my best tennis. It's maybe the biggest challenge in our sport to play Nadal at Roland Garros. I look forward to it, I'm happy to be here and motivated to win."