Littler blitzed Michael Smith 10-5 in the opening semi-final of the night before ripping apart Cool Hand Luke in a repeat of January's World Championship final.
World number one Humphries had beaten reigning Premier League champion Michael van Gerwen 10-5 earlier in the evening.
"I'm just enjoying it," victorious Littler told Sky Sports after receiving his trophy.
"I've been practising really hard and you can probably see it on the oche. I was dead focused, I didn't want to blink.
"I'm a major winner, I can put myself in that hat now.
"I can't wait to play in all the events. I've done so well on the Euro Tour and Pro Tour that I'm guaranteed to be in the Matchplay and Grand Prix."
"We'll (him and Humphries) meet in many finals - and now it's 1-1 in finals!"
Littler clocked up a stunning 10 180s in the final against Humphries, averaging a stunning 105.6, while Humphries was hitting 102.47 despite being on the wrong end of the result.
He also hit a superb nine-darter in the ninth leg, sending a record darts crowd of 14,000 into a frenzy.
The young star had finished top of the pile after 16 nights of the regular season, growing in confidence at the oche and in front of huge crowds as the campaign went on.
Yet he appeared in a much more focused mood on the night at the O2, rarely interacting with the crowd or engaging in any back-and-forths as he had in recent weeks.
Humphries was gracious as ever in defeat and spoke of his admiration of his opponent in the final.
"Tonight he was much stronger than I was and he deserved to win," runner-up Humphries told Sky Sports.
"And if you look at the season as a whole, he deserved to be Premier League champion.
"It's been a learning curve for me and for Luke as well. We both played our part in this tournament and I'm really proud to make the final.
"Of course I'm gutted not to win but you can't win everything. Six out of seven major finals for me now, I can only build on it.
"I'm proud of Luke, everyone knows what I think of him, I love him to bits, he's a great lad. I hope he enjoys himself and he deserves this moment."
As well as his first major trophy, Littler takes home £275,000 in prize money.