Still 19 days shy of his 17th birthday, Littler started a little nervously and lost the opening set but took control with an astonishing display of scoring and double-hitting.
He is by far the youngest player to reach the final of the championships and Cross, the 2018 champion, could only watch on and admire his fellow Englishman.
Littler won six successive legs after trailing for the first time in the tournament and was simply too clinical for his far more experienced opponent as he ran away to victory, sealing it with his trusty double 10.
"I have no words, it's just crazy to think I'm in a World Championship final in my debut. I was happy winning one game but I could go all the way," Littler told Sky Sports.
"Rob told me 'God bless, you're a step away, do it'.
"I've just settled on the stage. It took me a few legs to settle in the game and once I found that rhythm I was good to go."
Littler beat five-times world champion Raymond Van Barneveld 4-1 in the last 16 on Saturday before outscoring 50-year-old Brendan Dolan 5-1 in the quarter-finals on Monday.
"I'll do what I've been doing," Littler added. "In the morning I'll go for my ham and cheese omelette, then come here have a pizza and then practice on the board. That's what I've done every day.
"I'll be watching the other semi. I'm sure it will be another cracking game."
The English teenager will face Luke Humphries in the final on Wednesday after the world number three beat Scott Williams comfortably in the other semi-final.
No unseeded player has ever won the PDC World Darts Championship.
