Five-time World Grand Prix winner Van Gerwen stormed into the final with a ruthless straight-sets rout of Peter Wright, dropping just one leg in a one-sided contest.
Aspinall, meanwhile, battled past 2020 champion Gerwyn Price with a 4-2 success to hold off the Welshman's late rally and emotionally earn his first appearance in the World Grand Prix final.
Aspinall had taken a six-week break from the sport following the World Championship last December to undergo treatment for a serious wrist injury.
He has won two ranking events since returning to action in February, but has hit top form during the double-start World Grand Prix in Leicester this week.
Following victories over Michael Smith, Danny Noppert and Martin Lukeman, he ended world number one Price's bid to reach a third successive World Grand Prix final in sensational fashion.
Aspinall started the brighter and landed a 14-darter and a 113 finish as he claimed the opening set 3-1 in front of a sell-out crowd at the Morningside Arena.
Price finished 121 for a 12-darter on his way to the second set, but lost the third as Aspinall fired in a 13-dart leg as he moved ahead again in the match.
The fourth set was the first to go to a deciding leg as the opening four legs went with throw, but two missed darts at double 16 from Price allowed Aspinall in to land double five as he moved 3-1 up in the tie.
Aspinall then moved to the brink of victory in set five, leading 2-1 before Price levelled, and when the Stockport ace missed a match dart at double 16, the 2020 winner pounced with a 117 checkout to snatch the set and keep his hopes alive.
Price then took out 107 and 127 in successive legs to come from behind to lead in the sixth leg, but missed doubles allowed Aspinal in to level before a 13-darter saw him clinically close out the win.
2022 BoyleSports World Grand Prix Semi-Final results, Saturday October 8:
- Nathan Aspinall 4-2 Gerwyn Price (3-1, 1-3, 3-1, 3-2, 2-3, 3-2)
- Michael van Gerwen 4-0 Peter Wright (3-0, 3-0, 3-1, 3-0)
"To be in the BoyleSports World Grand Prix final, I'm absolutely on cloud nine," said Aspinall, who landed a clinical 56% of his finishing doubles in the tie.
"It means so much. I've put so much work in since my injury and worked so hard. Finally, I'm back in the final of a major and I'm buzzing.
"I think I should have won the game 4-1 but it wasn't to be - nerves took their toll on me and Gezzy, when he needed to, took some amazing shots out.
"I thought he was going to kick on and his double tops were going to start going, but it just didn't happen; I have no idea why and I'm thankful that I won."
Saturday's second semi-final proved a polar opposite as Wright endured a nightmare to lose 4-0 to rival Van Gerwen, winning only one leg.
Van Gerwen took out 167 in the game's opening leg and stamped his dominance on the tie by winning the first set without the World Champion having a dart at a finishing double.
BoyleSport World Grand Prix Grand Final, Sunday October 9:
- Nathan Aspinall v Michael van Gerwen, Best of nine sets
He also finished 94 and 98 to take command in set two, before punishing misses from Wright to double his lead in the tie.
Van Gerwen extended his winning streak to eight legs with checkouts of 67 and 54, before Wright finally got off the mark by taking out 73 to pull back to 2-1 in the third set.
The Scot, though, paid for missing his chance to level the set as Van Gerwen closed out the set to close in on another appearance in the final.
He then finished 124 to open the fourth set, landed double 16 to move 2-0 up and punished further misses from Wright to seal victory on tops.
"With my performance in the last few days I expected to win, but you still have to do it against a guy like Peter Wright," said Van Gerwen, who has also seen off Gary Anderson, Stephen Bunting and Chris Dobey in Leicester this week.
"He didn't look well and I don't know what happened there, but you need to take advantage of that.
"He's a phenomenal player but he didn't turn up tonight and I did the right things for myself at the right moment. Early doors I played well and that gave me confidence."
Van Gerwen has won the Premier League and World Matchplay this year, and has recovered from his own wrist surgery to return to top form and silence his doubters.
"I don't have to justify myself," he added. "Everyone knows what I'm capable of, and when Michael is there they're all scared.
"I have to win my games and I hope I can keep performing like this tomorrow as well.
"In winning the Premier League I didn't play my A-game, and I didn't really play my A-game in the World Matchplay but I still won it. Now I think I've played some decent darts and I'm really happy for myself."
Van Gerwen is the odds-on 3/10 favourite with sponsors BoyleSports going into Sunday's final, with Aspinall the 5/2 outsider to claim the £120,000 top prize and lift the new World Grand Prix trophy.
The tournament is being broadcast live on Sky Sports in the UK, through the PDC's worldwide broadcast partners including DAZN and Viaplay, and on PDCTV (excluding UK, Germany, Austria & Switzerland based subscribers).