The pair play each other for a 25th time, with Littler, 18, aiming for another major title after cruising into this final.
He decimated Jonny Clayton 5-1 on Saturday in the last four, after beating Mike De Decker, Gian van Veen, and Gerwyn Price in the earlier rounds.
Humphries, the world No1, beat Danny Noppert in his semi-final 5-3 to follow wins over Cameron Menzies and Chris Dobey.
The last time these two met was in New Zealand back in August, with Littler emerging the 8-4 victor.
What is the 2025 World Grand Prix darts prize money?
This evening, they play for £120,000, the winner’s share of the £600,000 prize fund of this competition. The runner-up walks away pocketing £60,000.
For those knocked out in the earlier stages, a first-round exit was worth £7,500, and the second round was double that at £15,000.
Reaching the quarter-finals netted players £25,000, and defeated semi-finalists earned £40,000.
