The contest at London's Alexandra Palace, with Littler bidding to become darts' youngest world champion, was viewed by a total of more than 4.8 million - making it the most watched darts event ever on Sky.
The previous peak record for a final of 1.65 million was set in January 2015 when Gary Anderson beat 16 times world champion Phil Taylor.
A peak audience of 2.32 million had already watched Littler's 6-2 semi-final thrashing of 2018 champion Rob Cross on Tuesday.
Humphries, who lived up to his "Cool Hand Luke" nickname, took the PDC World Championship with a 7-4 victory after reeling off five successive sets.
The world number one paid tribute to his young opponent afterwards.
"He's created a massive global following from so many incredible celebrities which is massive and great for our sport," Humphries told Sky.
"He well and truly could dominate the sport, that's for sure."
PARTY POOPER
Humphries, who took home a 500,000 pounds ($633,100) winner's prize, recognised the raucous crowd had wanted the teenager to win but said he had to "spoil the party".
He suggested also that Littler could change his nickname from 'The Nuke' to 'Relentless', so consistent and unfazed was his play.
"He made everything go his way. He showed such great maturity on young shoulders. If you are doing those sort of things at 16, it's mindless to think where he could be in five years' time.
"He will be world champion one day, there is no doubt in my mind. I just thought to myself its important that I get one in early before he does dominate us all and it becomes a much harder task to beat him."
Littler told a press conference he had enjoyed every minute of the competition but was also looking forward to going home and "getting back to reality".
Britain's Prime Minister Rishi Sunak sent a congratulatory message via X, although some questioned when the "Congratulations Luke, a great win tonight" had actually been written.
"When I look on Facebook and someone's tagged me in to say there's people around my house, it doesn't look good does it?," said Littler of all the 'darts mania' triggered by his rise to the top.
"But it should die down and I hope it does die down because I just want to go home with no-one really near my house or anything."
